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Leaky sewers cause hidden nutrient pollution in German urban waters

March 26, 2021
Sewers under Berlin, Germany. Image: SnaPsi | Flickr Creative Commons

A growing body of research suggests that untreated wastewater leaking from damaged or badly designed sewer systems is a key source of urban water pollution. However, data on sewer leaks and pollution is often missing from large-scale environmental assessments of urban areas.

A new study by Dr. Hong Hanh Nguyen and Dr. Markus Venohr from the Leibniz Institute of Freshwater Ecology and Inland Fisheries (IGB) in Berlin responds to this deficit. The authors propose the first German national estimation of wastewater losses from defective sewer systems by bringing calculations of sewer leaks into urban catchment models.

“Sewer systems are hidden in the ground and perform an important – but often unrecognised – job to collect wastewater ahead of its subsequent treatment,” says co-author Dr. Markus Venohr. “Damage to sewer systems, and any potential leaks into surrounding ground, are often hard to detect and quantify,” Dr. Venohr explains. “As a result, these aspects are usually neglected in large-scale nutrient emission modelling.”

The researchers upscaled local calculations of sewer leaks to both pipe, city and municipality scales using a combination of datasets and expert knowledge. They found that pollution from sewer leaks is found across both public and private sewers, but is particularly common in ageing pipes more than 40 years old.

“In our new paper, we calculate the contribution of losses from leaking sewer systems to overall Germany-wide nutrient emissions,” Dr. Venohr continues. “We discuss these nutrient losses within the framework of the LAWA-funded project AGRUM-DE, to which our work makes an important contribution.”

“Our study shows that sewer age and type, together with human population density, are key factors influencing the potential for sewer losses from public and private sewers,” says Dr. Venohr.

One key finding from the study is that water pollution from leaking sewers might account for between 10–20% more nutrient loads entering groundwater from urban areas across Germany than previously calculated.

“Overall, sewer leaks were estimated to locally add a substantial share of nutrient emissions from urban systems to groundwater, and thus to surface waters,” Dr. Venohr outlines.

The study stresses the importance of addressing leaky sewer systems as a potentially significant source of water pollution in urban environments. The authors suggest that their study framework will allow environment managers to better target pollution sources and incorporate leaky sewers as part of the long-term nutrient water management of agricultural and urban emissions.


Nguyen, H.H., Venohr, M. Harmonized assessment of nutrient pollution from urban systems including losses from sewer exfiltration: a case study in Germany. Environ Sci Pollut Res (2021).

Towards a freshwater ethic: lessons from Aldo Leopold for contemporary aquatic conservation

March 10, 2021
Aldo Leopold on a trip to the Rio Gavilan watershed in Mexico’s northern Sierra Madre Occidental. It was here that some of his key ideas about land and water conservation were formed in the 1930s. Image: Pacific Southwest Forest Service, USDA | Flickr Creative Commons

“All ethics so far evolved rest upon a single premise: that the individual is a member of a community of interdependent parts. The land ethic simply enlarges the boundaries of the community to include soils, waters, plants and animals, or collectively the land.” This is the core of early-20th Century American conservationist Aldo Leopold’s outlook on environmental management, or as it his commonly known, his ‘land ethic’.

Writing in his seminal A Sand County Almanac, published in 1949, Leopold outlines a gently-radical ecosystem-orientated approach to natural resource management, in which humans are encouraged to foster a responsible and sustainable relationship with the biotic communities with whom they share a landscape. The book, which in a series of essays documents the ecosystems on Leopold’s farm in Wisconsin, and more widely in the USA, Canada and Mexico, is a landmark text in the development of the American (and arguably, global) conservation movement. In no small part due to its lyrical tone, A Sand County Almanac is also widely cited as popularising public debates in both ecology and environmental ethics.

The ‘land’ in Leopold’s land ethic leads a casual reader to assume that he was solely interested in terrestrial ecosystems. However, as the quote above shows, Leopold’s land ethic explicitly includes a responsibility towards the conservation of aquatic ecosystems. Indeed, Leopold was a keen angler, and wrote about the sustainable management of rivers and streams, particularly in terms of the impact of soil erosion and run-off as a result of poor land management.

More than half a century later, then, could Leopold’s work be used to develop a ‘freshwater ethic’ which could strengthen contemporary aquatic conservation? According to a team of freshwater researchers writing in the Aquatic Conservation journal, there is rich potential to rediscover Leopold’s work in this way.

The team, led by Prof. Steven J Cooke from Carleton University, Canada, reflect on Leopold’s scholarship to identify a set of ‘Aldo-inspired’ recommendations for protecting and restoring freshwater ecosystems in an Anthropocene era. These include: adopting an ecosystem approach; managing freshwaters as coupled social-ecological systems; acknowledging the limits to human dominance over freshwater systems; and addressing the underlying causes of environmental issues rather than their symptoms.

“2020 was the 70th anniversary of Aldo Leopold’s land ethic,” says Prof. Cooke. “That seemed like an opportune time to take a pause and reflect on what the land ethic has meant in terms of aquatic conservation and consider how it could be used to explicitly define a freshwater ethic.”

“There are few ecologists and nature conservationists whose thinking has not been touched, or even inspired, by Aldo Leopold: the ethical notions that love and respect for the natural environment stem from a perspective in which ‘land is a community to which we belong’; that our action is ‘right when it tends to preserve the integrity, stability and beauty of the biotic community,’” says co-author Prof. Steve Ormerod from Cardiff University. “Although stated often as a ‘land ethic’, Leopold’s boundaries embraced soil and water as much as they embraced plants and animals: an environmental whole of which we are citizens.”

“One of Leopold’s first peer reviewed papers was in Transactions of the American Fisheries Society and he was responsible for the management of aquatic resources at various times in his career. It is easy to think of Leopold as being concerned about land and terrestrial wildlife but his definition of both was inclusive in many ways and he certainly understood the interconnections between land and water,” Prof. Cooke says.

Aldo, Carl, and Estella Leopold beside the Wisconsin River. Image: Aldo Leopold Archives.

The journal authors argue that Leopold’s outlook has significant value for contemporary freshwater management. This is reflected in their ‘Aldo-inspired’ recommendations, which also include: acting now to address the biodiversity crisis, even when faced with uncertainty; identifying ‘win-win-win’ scenarios in which the value of clean water is shown to have wide societal benefits; and the vital nature of ‘wild’ or barely-modified rivers.

Moreover, the authors look to Leopold to remind us that freshwaters are a core element of diverse human-nature relationships, and a sense of ‘freshwater optimism’ is necessary to make positive conservation progress. On this point, the authors quote Leopold on his conservation philosophy, writing in 1938 that, “We shall never achieve harmony with the land, anymore than we shall achieve absolute justice or liberty for people. In these higher aspirations the important thing is not to achieve but to strive.”

“The plight of freshwater ecosystems – now some of the most threatened on earth – motivated us to re-emphasise Leopold’s holistic view in our paper,” states Prof. Ormerod. “Human actions around freshwaters so often reflect a careless assumption that rivers and lakes exist for drinking water, for waste disposal or for hydropower. Or that wetlands can be drained for development without thought for the consequences. Freshwater ecosystems are critical to our survival – and Leopold reminds us not only of our ethical responsibility towards them, but that our own fate will be tied to theirs.”

“Today A Sand County Almanac remains on the reading list in many natural resource management programs,” says Prof. Cooke. “It is our hope that our essay will help to inspire the next generation of aquatic biologists and managers to consider Leopold’s wisdom and apply his principles to contemporary conservation problems.”


Cooke, SJ, Lynch, AJ, Piccolo, JJ, Olden, JD, Reid, AJ, Ormerod, SJ. Stewardship and management of freshwater ecosystems: From Leopold’s land ethic to a freshwater ethic. Aquatic Conserv: Mar Freshw Ecosyst. 2021; 1– 13.

World’s ‘forgotten fishes’ in catastrophic decline

February 23, 2021
Snorkelling in a river in Western Cape, South Africa. Image: Jeremy Shelton

Nearly a third of global freshwater fish species are threatened by extinction, according to a major new report compiled by 16 conservation groups.

Released today, The World’s Forgotten Fishes report states that 80 species of freshwater fish are known to have gone extinct, with 16 of these extinctions occurring in the last year alone. Since 1970, populations of migratory freshwater fish have fallen by 76%, and large ‘megafauna’ fish species by a startling 94%.

The report, published by a coalition of groups including WWF, IUCN, and the Alliance for Freshwater Life, highlights the rich variety of global freshwater fish species: the current known total of 18,075 species accounts for over half of all the world’s fish species, and a quarter of its vertebrate species.

However, despite the vital role these fish species play in human health, food security, livelihoods and culture for communities across the world, many of their populations are in critical decline. Common threats to freshwater fish include habitat destruction, hydropower dam construction, agricultural and industrial pollution, and climate change. In some regions, overfishing, poaching and invasive species are also key pressures.

The Iznajar hydropower dam in Spain. Dam construction is one of the key threats to freshwater fish populations in global rivers. Image: Global Warming Images / WWF

“Nowhere is the world’s nature crisis more acute than in our rivers, lakes and wetlands, and the clearest indicator of the damage we are doing is the rapid decline in freshwater fish populations. They are the aquatic version of the canary in the coalmine, and we must heed the warning,” says Stuart Orr, WWF Global Freshwater Lead.

“Despite their importance to local communities and indigenous people across the globe, freshwater fish are invariably forgotten and not factored into development decisions about hydropower dams or water use or building on floodplains. Freshwater fish matter to the health of people and the freshwater ecosystems that all people and all life on land depend on. It’s time we remembered that,” Orr argues.

The report is published only days after a paper in the journal Science shows that half of all global river systems have been significantly impacted by human activities, with only very large tropical basins subject to lower levels of alteration. The study, by Dr. Guohuan Su and colleagues, states that freshwater fish biodiversity has become homogenised in many river basins due to human alterations, primarily river fragmentation and the introduction of non-native species.

Freshwater fish are part of vital aquatic ecosystems, providing prey for predators such as this giant otter in the Pantanal, Brazil – the world’s largest tropical wetland. Image: R.Isotti, A.Cambone / Homo Ambiens / WWF

However, despite the declining trends in freshwater fish populations across the world, The World’s Forgotten Fishes ends on a hopeful note. It argues that 2021 is a crucial year to address the freshwater biodiversity crisis, through implementing the tenets of the WWF-led Emergency Recovery Plan into a New Deal for Nature and People ahead of the UN Convention on Biological Diversity (CBD) conference held in Kunming, China in May.

“The good news is that we know what needs to be done to safeguard freshwater fishes. Securing a New Deal for the world’s freshwater ecosystems will bring life back to our dying rivers, lakes and wetlands. It will bring freshwater fish species back from the brink too – securing food and jobs for hundreds of millions, safeguarding cultural icons, boosting biodiversity and enhancing the health of the freshwater ecosystems that underpin our well-being and prosperity,” states Orr.

“What we need now is to recognise the value of freshwater fish and fisheries, and for governments to commit to new targets and solutions implementation, as well as prioritising which freshwater ecosystems need protection and restoration. We also need to see partnerships and innovation through collective action involving governments, businesses, investors, civil society and communities,” concludes Orr.

Freshwater fish populations are crucial sources of food and livelihood to many communities across the world, including this fisherman on the Luangwa River, Zambia. Image: James Suter / Black Bean Productions / WWF-US


Read The World’s Forgotten Fishes report.

Wetlands: Havens of Life

February 11, 2021

Last week communities around the world celebrated World Wetlands Day, an event held to raise global awareness about the vital role of wetlands in supporting biodiversity and human wellbeing.

During online conversations around the event we discovered a fascinating short film titled ‘Wetlands: Havens of Life’. The film, made by author Julian Hoffman in collaboration with The Wetlands Initiative, documents the rich cultural and ecological diversity of the Prespa Lakes in Southern Europe.

Julian is an award-winning landscape writer who has lived in the Prespa Lakes region since 2000. His most recent book Irreplaceable: The Fight to Save our Wild Places explores vital conservation and restoration projects in imperilled ecosystems across the world. We spoke to Julian to find out more about his film, the Prespa Lakes, and the value of wetlands.


Tell us a little about the Prespa Lakes – what makes them special?

The enduring image of Greece will always be of islands, seas, whitewashed villages and ancient ruins, but there is a whole other country of diverse landscapes beyond that iconic picture, which includes a place like Prespa. The Prespa Lakes – Great and Lesser – sit encircled by high mountains in the far north-west corner of Greece. Not only are they ancient lakes, and amongst the oldest in the world, but they are also shared by three countries – Greece, Albania and North Macedonia. And it’s this being at a crossroads – both culturally and geographically, as they’re a connecting point between Mediterranean and Balkan alpine ecosystems – that lends them such a distinctive quality.

Along with supporting varied human communities around their shores, they host a remarkable range of wildlife. Large numbers of waterbirds, including night herons, little bitterns and squacco herons, nest in the vast reedbeds of Lesser Prespa Lake. Of the 23 species of fish found in Prespa’s lakes and rivers, 9 of them are endemic to the region. And Prespa is home to around 1,400 pairs of Dalmatian pelicans, making it the world’s largest colony of a species officially listed as Near Threatened, where these remarkable birds nest alongside some 600 pairs of white pelicans too. The Prespa lakes are a place of unique ecological and cultural richness.

Prespa Lakes. Image: Julian Hoffman

What is your connection with the lakes and the wider region?

My wife and I moved to a small mountain village above the lakes in the Greek part of Prespa back in 2000 after reading Giorgos Catsadorakis’ excellent and evocative book Prespa: A Story of Man and Nature while we were living in London. Two decades later and we’re still here, partially because the place has such a compelling ability to continually fascinate and surprise. It’s a very rural place, yet at the same time it’s beautifully cosmopolitan too, being a gathering place for different cultures, languages, histories, habitats and species.

Much of my writing about the natural world and our human connection to place has emerged out of a relationship with the lakes region, and my wife works for the Society for the Protection of Prespa, a local environmental organisation that has been instrumental in protecting the lakes’ natural and cultural values for the past three decades. They work closely with the local community, and part of my wife’s work involves a transboundary network called PrespaNet, which brings together environmental organisations from the three countries that share this watershed. While these countries have long had their political and historic differences, seeing the cross-border engagement between organisations and ecologists around common issues of water, climate and biodiversity is profoundly positive, reminding us of the many commonalities that borders tend to obscure.

How did you become involved with The Wetlands Initiative? What work does the organisation do, and why is it important?

I came to know about The Wetlands Initiative (TWI) when I spent some time at the Midewin National Tallgrass Prairie just outside of Chicago while researching my recent book, Irreplaceable. This prairie – which is now a beautiful and beguiling blend of grasslands and wetlands – had been restored from a sprawling military ammunition depot, where the US government manufactured and stored extraordinary amounts of ordnance over the course of several decades. As a result, the land was largely ruined. But there was a vision to heal it, and when the government officially passed the land into the care of the US Forest Service, TWI was at the heart of the ensuring actions, making possible an extraordinary transformation.

It was the first time I’d ever witnessed a large-scale ecological restoration project and I was overwhelmed by the dramatic changes. The songs of chorus frogs pulsed from the marshes and bison grazed the grasslands as they would have done in the past. It had the feel of a world being remade. Midewin is a stunning and inspiring testament to what is possible when we channel our energies towards a respectful relationship with the natural world. And TWI’s overarching mission to restore wetlands in both Illinois and Indiana, including on the South Side of Chicago, where local communities have lacked access to green spaces because of industrial and residential sprawl, means there’s a greater chance that a positive future for both humans and wildlife can unfold in those places.

Pelicans on Prespa Lakes. Image: Julian Hoffman

Tell us about making your ‘Wetlands: Havens of Life’ film at Prespa – what was the catalyst for its production, and what did you want to communicate with it?

Last year I was supposed to give a talk for TWI in Chicago as part of their 25th anniversary festivities. The event was naturally cancelled because of the pandemic, but we still had this deep desire to honour and recognise this achievement and to find some way of celebrating it and the larger meaning of wetland protection and restoration. It was then that TWI asked me whether I’d be interested in making a film about wetlands here in Prespa. As my focus for the talk would originally have been on the work of TWI, it meant suddenly recalibrating my attention back to my home place. But in a way that made complete sense, because while in some respects this terrible pandemic has emphasised the distance between us, it has also revealed a greater sense of solidarity, too. And while the wetlands I live beside in Greece are a very long way from the ones TWI works with in the American Midwest, we share a love for them that acts as a bridge.

I think with the film we wanted to communicate the idea that no matter where in the world wetlands are found, they are part of a much larger network of waters that nourishes a wide spectrum of wildlife, habitats and human communities. It’s these many complex connections, in a sense, that make us all tributaries when it comes to the greater meaning of wetlands, linking us together through water.

Following the insights of your Irreplaceable: The Fight to Save our Wild Places book, what might wetland conservation and restoration tell us about environmental management and ethics in an Anthropocene age?

A few years ago, I traced autumn bird migration from the south of Spain to Morocco to see what traditional salt pans meant for journeying birds. My final destination was a set of salt pans being restored near the Moroccan town of Larache. The pans and lagoons had been closed a number of years earlier by their owner, effectively shutting down an important staging post for migratory birds, which, according to the ecologist I spent time with there, had a record of hosting 15,000 glossy ibises in a single day. Since they’d shut, however, he said that almost no birds stopped there anymore. But on the day we arrived, as water was beginning to flow once more, providing vital jobs for the local community and restoring a relationship between that place and migratory birds that had been severed as soon as the waters evaporated, the wetland was thriving with birds again. Avocets, storks and godwits. Ospreys, redshanks and herons. Egrets, spoonbills and glossy ibises, too. It was an extraordinary spectacle of life and movement to see, especially given the description and photos the ecologist had given me that depicted the place only a few years earlier when it was dry. And what it made we realise is how actions that might seem small in the larger scale of things can have profoundly transformative effects.

For the poor community of labourers that lived by the lagoons, a vital opportunity for livelihood was viable once more. For the thousands of birds feeding there that day, their safe journey across the Sahara or survival over winter on the African coast was made more likely. Neither the wellbeing of humans nor the wellbeing of wildlife needs be to the exclusion of the other. I think it’s imperative that we enlarge our sense of home so that it includes the more-than-human in its embrace. And wetlands are good examples of the possibilities that arise when we do, whether that’s here beside two ancient lakes in the Southern Balkans or on a set of small restored salt pans in Morocco. It’s the intention at the heart of the gesture that matters.


Julian Hoffman website.
‘Restoring Wetlands: a path into the future’ essay for the 25th anniversary of the Wetlands Initiative in 2020.

Act now to mitigate climate change impacts on aquatic ecosystems, scientists urge

January 29, 2021
The River Rhine in Germany: climate change is predicted to increasingly impact global aquatic ecosystems in coming years. Image: Arno Hoyer | Flickr Creative Commons

The effects of climate change will cause severe environmental and humanitarian crises in years to come unless globally-concerted climate actions are urgently implemented, according to a coalition of over 100 aquatic science societies. The effects of climate change are particularly severe in marine and freshwater ecosystems, the scientists say, potentially causing significant losses in aquatic biodiversity, fisheries and human livelihoods, unless effective mitigation actions are taken.

In a statement recently published on the American Fisheries Society website, the coalition representing more than 80,000 global scientists state, “It is time to acknowledge the urgent need to act to address climate change. Delaying action to control greenhouse gas emissions is not an option if humankind wishes to conserve the aquatic resources and environmental safety of the world.”

The statement synthesises cutting-edge scientific research into succinct diagnoses of contemporary aquatic conservation issues. As readers of this blog will likely know all too well freshwaters are among the most threatened ecosystems on Earth, covering less than 1% of the planet, but supporting one-third of all vertebrate species and 10% of all species.

Climate change is already causing significant environmental impacts on freshwaters, and predictions suggest many of these will increase in severity in the future. These impacts are wide-ranging: altered ecological food webs, increased frequency and intensity of droughts, invasive species, shifting climatic niches of many plants and animals, reductions in wetland capacity to store carbon, and increased incidences of algal blooms, amongst many others. These are only a few common issues, and, as contemporary research on multiple stressors in freshwaters tells us, the stresses they place on ecosystems can interact to intensify their individual impacts.

The scientists’ statement emphasises that mitigating climate change impacts is crucial, not only for conserving freshwater ecosystems themselves, but also in supporting human livelihoods which depend on the many services freshwaters provide. Key issues here include the provision of fisheries, drinking and cleaning water, tourism, carbon sequestration and natural flood protection.

2021 is an important year for global climate action. In November, world leaders will meet in Glasgow for the successor to the landmark 2015 UN Climate Change Conference in Paris. Where the Paris agreement brought together most of the world’s nations to agree to tackle climate change for the first time, the 2021 Glasgow COP26 meeting offers the opportunity for nations to pledge to further cut their carbon emissions. Indeed, pledges to reach net-zero carbon emissions from China, Japan and South Korea are already nearing the Paris 2015 targets.

The scientists’ statement is intended to offer a voice for aquatic life in these debates, emphasising that freshwater and marine ecosystems are not only at risk from ongoing climate change, but that their natural functioning provides numerous climate mitigation and human livelihood benefits to society. They call for, “Governments, the public, industry, academia, and all other sectors of society [to] prioritize actions and act in a concerted way to halt human-caused climate change if they are to prevent dire consequences.”


Read the statement in full on the American Fisheries Society website here.

Multiple stressors shape river ecosystems across Europe

January 22, 2021
The River Douro in urban Porto, Portugal. Multiple stressors from human activities are significantly impacting European river ecosystems. Image: Terry Kearney | Flickr Creative Commons

In recent years, freshwater scientists across the world have explored how the ecological health of rivers and lakes is impacted by multiple human stressors. Such stressors – for example, pollution, water abstraction, bank alterations and habitat loss – often act in complex combinations, which can variously intensify or reduce their individual impacts.

Freshwater managers and conservationists have long known that aquatic ecosystems are affected by a wide range of human activities, but until recently there has been little evidence-based guidance on how to manage for their impacts. Recent multiple stressor research seeks to untangle how different stressors interact, the impacts they can have, and the management actions that are most effective for tackling specific multiple stressor combinations.

Despite the recent upsurge in multiple stressor studies, there are still significant unanswered questions in the field. One key issue is upscaling results from experiments on aquatic biota based on a small number of stressors to larger – catchment and continental – scales which are useful for shaping management and policy decisions.

A new study providing the first overview of how multiple stressors determine ecological status in European rivers aims to address this shortfall. The study, by Jan U. Lemm from the University of Duisburg-Essen and colleagues from the MARS and SOLUTIONS projects, links the intensity of seven stressors to recently measured ecological status data for more than 50,000 river sub-catchments. Using data from the reporting of Water Framework Directive River Basin Management Plans between 2010-2015, the modelling study area covers almost 80% of Europe’s surface area.

The study, published in the Global Change Biology journal, shows that stressors account for an average of 61% of deviance in ecological status across twelve different river types in Europe. In other words, almost two-thirds of the observed variations in European freshwater biota can be directly attributed to human impacts.

Hydro-morphological, nutrient and toxic stressors are three dominant factors in determining the health and status of European river ecosystems. Image: Lemm et al 2021

“Our work shows the hierarchy of multi-stressor impacts on Europe’s rivers: various hydro-morphological alterations affect aquatic ecological status most severely, followed by nutrient and toxic stress. The latter clearly demonstrates the distance to Europe’s target of a non-toxic environment, called for by the Green Deal,” says co-author Dr. Sebastian Birk from the University of Duisburg-Essen.

More than half of the variances in ecological status can be explained by multiple stressor interactions, according to the scientists’ models. Pollution of rivers from nutrients and toxic substances are the stressors which interact most frequently and strongly, the authors state.

Dr. Birk says the study findings should call attention to the urgent need to reduce human impacts on freshwater ecosystems. “Ecological impacts are mainly driven by stressor interactions, underlining the intricate interplay of human activities on the environment. This is just more evidence for the need of transformative change in the way we deal with nature… the science is unmistakeable, but are we ready to change?”

“This paper represents one of the first approach to link multiple stressors and their effects on the ecological status at European scale,” says co-author Dr. Markus Venohr from the Leibniz-Institute of Freshwater Ecology and Inland Fisheries (IGB). “An important pre-condition was to derive all stressors and conduct analyses at the spatial scale of the status information reported by member countries.

“By mapping near-natural and managed flow conditions and by directly including nutrient emissions, the effects of human uses on ecological status can be revealed. These relationships are often unrecognised at smaller scales due to lower gradients and smaller numbers of cases. We are positive that this work can provide a major development for a harmonised effect assessment and for improving measure efficiency to reach the goals of the EU Water Framework Directive,” Dr. Venohr says.

The study suggests that there are common environmental stressors affecting all European freshwaters, regardless of region or river size. Although stress intensity varies geographically, all European river types are affected by riparian land use, hydrological alterations, nutrient enrichment and toxic substance pollution.

The study authors state that their findings should prompt water managers and policy makers to adopt more holistic approaches to freshwater assessment and management. Such approaches, which link both small- and catchment-scale management, and explicitly consider the impacts of multiple stressors – are crucial if the ambitious targets of the European Water Framework Directive are to be reached, and the health of European freshwaters is to be restored.


Lemm, J.U., Venohr, M., Globevnik, L., Stefanidis, K., Panagopoulos, Y., van Gils, J., Posthuma, L., Kristensen, P., Feld, C.K., Mahnkopf, J., Hering, D. and Birk, S. (2021), Multiple stressors determine river ecological status at the European scale: Towards an integrated understanding of river status deterioration. Glob Change Biol. Accepted Author Manuscript.

Top 10 posts of 2020

January 2, 2021
Winter stream in Telemark, Norway. Image: Thor Edvardsen | Flickr Creative Commons

In these early days of the new year we delve back through our top ten posts published in 2020.

It is an understatement to say that 2020 was a strange and unprecedented year for everyone. Thank you for reading: despite everything, there was some fascinating and important freshwater research published in 2020, alongside a significant rise in policy advocacy campaigns seeking to gain traction for freshwater issues. You can explore all of last year’s posts here.

We send you best wishes from everyone at the Freshwater Blog: here’s to a happier and healthier 2021.


Eavesdropping on underwater worlds: the potential of aquatic ecoacoustics (January)

Acoustic Ecologist Dr Simon Linke, who co-edited the special journal issue on aquatic ecoacoustics. Image: Griffith University

Could listening to the underwater sounds made by freshwater life help us better document and protect aquatic ecosystems? A new special issue of the Freshwater Biology provides intriguing evidence to suggest that it could. Acoustic monitoring has emerged as a key tool for ecologists and conservationists in recent years. Bioacoustics (the study of sounds produced by or affecting living things) and ecoacoustics (the study of environmental sounds relating to ecosystem processes) continue to grow in popularity as approaches to ecological monitoring. However, the use of such acoustic monitoring techniques has yet to be fully explored or adopted in freshwater systems. The new special issue, edited by Dr Simon Linke, Dr Camille Desjonqueres and Dr Toby Gifford, outlines the opportunities acoustic monitoring offers to freshwater researchers and conservationists, in an effort to raise awareness of its potential. (read more)


An Emergency Recovery Plan for global freshwater biodiversity (February)

2020 could be a pivotal year for the future of Earth’s biodiversity. In November, the world’s governments will meet at the Convention on Biological Diversity (CBD) conference to agree a new global deal to conserve and restore biodiversity. A major new scientific paper published in BioScience last week outlines an Emergency Recovery Plan for freshwater biodiversity declines, designed to influence discussions at the CBD conference in November. Developed through collaborations between scientists from WWF, International Union for Conservation of Nature (IUCN), Conservation International, Cardiff University and other institutions, the paper outlines a six-point plan to ‘bend the curve’ of global freshwater declines. (read more)


Are Pablo Escobar’s hippos restoring ‘lost’ ecological processes to Colombian freshwaters? (April)

A herd of hippopotamuses swim in a muddy lake at Pablo Escobar’s abandoned estate in northern Colombia. A new study suggests that these hippos may be restoring ‘lost’ ecological processes not present since the Late Pleistocene era. Image: | Flickr Creative Commons

When Pablo Escobar died in 1993, the drug kingpin left behind – amongst other things – a private zoo on his Hacienda Nápoles estate in northern Colombia. Whilst Escobar’s elephants, lions, giraffes and other animals were transported to other zoos when the estate was seized by the Colombian government after his death, four hippopotamuses were left behind. The hippos – of which Escobar was said to be particularly fond – were deemed too dangerous and aggressive to move, and were left where they were. As the estate became neglected and overgrown, the hippo population at Hacienda Nápoles grew, gradually colonising artificial lakes and the Magdalena River. (read more)


Freshwater life in the time of COVID-19 (May)

The Lena River Delta, Russia. Image: Daniel Coe | Flickr Creative Commons

Life has been strange for all of us over this last couple of months. From all of us at the Freshwater Blog, we wish you and your loved ones all the best during these difficult times. Given that lots of us have limited opportunities to visit, enjoy and learn about rivers and lakes right now, we thought this week’s blog would collate some of the digital ways we can immerse ourselves in freshwater life, at least for the time being. (read more)


The EU Biodiversity Strategy for 2030: five issues for the future of freshwater ecosystems (May)

Wilczka River, Poland. Image: Tomasz Przywecki | Flickr Creative Commons

Earlier this week the European Commission published a new Biodiversity Strategy, designed to tackle the key drivers of biodiversity loss by 2030, both in Europe and globally. Released during the ongoing COVID-19 pandemic, the document is framed as a key element of the EU’s recovery plan – aiming to boost both ecological and economic resilience through policy and management. Along with the linked Farm to Fork Strategy, the new EU Biodiversity Strategy for 2030 aims to designate at least 30% of European land and seas as protected areas, and to ensure that at least 10% of the continent’s agricultural land is managed as ‘high-diversity landscapes’ by 2030. Funding of around €20 billion per year has been designated to help meet this target, translated into policy through the ambitious EU Nature Restoration Plan. Clearly, there is a lot in the Biodiversity Strategy to feel hopeful about. But what place do freshwater ecosystems have in its plans? We take a look at five key issues. (read more)


Ecological surprises: how do multiple stressors impact European rivers and lakes? (June)

Multiple stressors from human activity on the Emscher River, Germany. Image: Christian Feld

Guest blog by Sebastian Birk and Daniel Hering

When does 1+1=3 for freshwater conservation and restoration? What seems like a trick question is actually the basis of a major European research project, MARS, begun in 2014. The 1’s in the equation refer to single stressors on freshwater ecosystems – things like nutrient pollution, water abstraction and temperature increases. Adding the effects of single stressors together should give us an indication of the overall stress placed on the ecosystem by human activities, shouldn’t it? Not always! (read more)


Half of known freshwater megafauna species threatened with extinction (July)

The Beluga, or European sturgeon. Image: Charlene N Simmons | Flickr Creative Commons

Many of the largest and most iconic freshwater species in the world are threatened with extinction. There are around 200 species of such ‘freshwater megafauna’ – species weighing more than 30kg, and found on every continent except Antarctica – of which 34 species are listed as Critically Endangered by the IUCN Red List, and half are classified as Threatened. Freshwater megafauna such as the beluga sturgeon, American alligator, Yangtze finless porpoise, and Caspian seal often have complex life cycles and extensive habitat requirements. As such they are sensitive to habitat loss, over-harvesting and river fragmentation. A recent study found that freshwater megafauna declined by 88% globally between 1970 and 2012, with a 94% decline in megafauna fish species. (read more)


84% of global freshwater species populations lost since 1970: can we ‘bend the curve’ of this trend? (September)

The Yangtze River in China – home of the Chinese sturgeon, populations of which have declined by 97% since 1982 due to habitat degradation. Image: Boris Kasamov | Flickr Creative Commons

Global populations of mammals, birds, amphibians, reptiles and fish have, on average, declined by two-thirds since 1970, according to the latest WWF Living Planet Report, released earlier this month. Continuing the trends shown in past reports, freshwaters are particularly imperilled: with 84% of global freshwater species populations lost between 1970 and 2016. WWF have published a Deep Dive into Freshwater’ document looking at the stark findings of the Living Planet Report, and outlining ways to support global freshwater conservation in their wake. The publication states that population declines are particularly acute among freshwater amphibians, reptiles and fishes. Whilst freshwater population declines have been observed globally, they are most severe in Latin America and the Caribbean. (read more)


Safeguarding freshwater life beyond 2020: 14 recommendations for environmental policy (October)

A headwater stream in the Austrian Alps. Image: Theo Crazzolara | Flickr Creative Commons

Freshwater biodiversity is in a critical state of decline across the world, as startlingly shown in the most recent WWF Living Planet report. This year, updates to two international policy frameworks which could have significant influence on the future of freshwater life – the Convention on Biological Diversity (CBD) and the European Union (EU) Biodiversity Strategy – are being prepared. How can we ensure that global freshwater biodiversity is properly valued and protected by these frameworks over coming decades? An international research team led by Dr. Sonja Jähnig at the Leibniz Institute of Freshwater Ecology and Inland Fisheries (IGB) in Germany have published a journal paper containing 14 key recommendations for the global protection of freshwater biodiversity. Their aim is to encourage decision makers to ensure that both the post-2020 CBD Global Biodiversity Framework and the post-2020 EU Biodiversity Strategy better account for freshwater ecosystems. (read more)


A global digital observatory of Earth: exploring the potential of culturomics and iEcology for aquatic conservation (November)

Online images, videos and audio of the natural world are being used by conservationists to track changes in global ecosystems. Image: Cindy Shelbey | Flickr Creative Commons

The natural world has never been more closely documented than it is today, not only in scientific studies but also in the public use of digital technologies to capture and share their daily lives. Photographs, videos and audio recordings of nature shared on social media and other online platforms could provide valuable ‘big data’ resources for aquatic conservation, according to the authors of a new journal article. “These are kinds of data that are produced as a by-product of our daily lives. Someone’s online snorkelling video could help ecologists understand which reef species are present, or the behaviour of recreational users relative to particularly sensitive species,” explains Professor Kate Sherren, a co-author of the study from Dalhousie University, Canada. (read more)


Thanks for reading, and a happy 2021 to you! If you are in need of more freshwater stories, you can read our previous annual post round-ups for 2019, 2018, 2017 and 2016.

More than one million barriers fragment Europe’s rivers

December 18, 2020
Vidrau hydroelectric dam on the Argeș River, Romania. Image: Jarom Irkavan | AMBER

European rivers are fragmented by at least 1.2 million barriers, which can significantly alter their flow and habitat provision, according to an ambitious new study published this week. The results, issued in Nature, suggest that Europe has some of the most fragmented river systems in the world, with an estimated 0.74 barriers per kilometre of river.

River fragmentation is not only the result of large dam and hydropower constructions. Instead, the research team, coordinated by the Horizon 2020 AMBER project, mapped thousands of smaller structures such as weirs, culverts, fords, sluices and ramps in rivers across the European river network.

These structures fragment river systems in different ways, often affecting their flow, course and links with wider floodplains. This variety in impacts extends to ecosystem processes, too: some structures may affect the movement of fish and insect species but barely impact nutrient and sediment flows, or vice versa. Just to add to this complex picture, these barrier impacts can often be highly variable in scale across time and space.

These are key issues for European river managers seeking to conserve and restore their catchments after decades of modifications for energy production, industry, agriculture, urban growth and flood protection. As the authors of the new paper outline, there is a shortfall in knowledge about where river barriers are located in European rivers, and the variable impacts they have on fluvial dynamics and aquatic biodiversity.

“The extent of river fragmentation in Europe is much higher than anyone had anticipated,” says Barbara Belletti, a river geomorphologist who led the study at Politecnico di Milano and is now at CNRS, the French National Centre for Scientific Research.

European river basins mapped by colour. Image: AMBER from ECRINS data, EEA, Copenhagen, 2012

Belletti and colleagues carried out the mammoth task of mapping European river barriers in three steps. First, they compiled barrier records across the 1.65 million km long European river network from 120 local, regional and national databases. Second, they ‘ground truthed’ this data by walking around 2,700km of the river network in 26 countries during low-flow conditions. This allowed them to record the location and characteristics of river barriers, and to address errors or omissions in the existing data. They found that not one of the 147 rivers they surveyed in person was free of obstructions. Third, the research team extrapolated their data to estimate barrier densities in regions with poor and patchy datasets.

Their study maps around 630,000 river barriers across Europe – largely ramps, bed sills, weirs and culverts. As you might expect, the highest barrier densities are found in the heavily modified river systems of Central Europe, and the lowest densities in more remote and sparsely populated regions. This work is illustrated in the AMBER Barrier Atlas, the first comprehensive river barrier map of Europe.

“Over 100,000 of these barriers are obsolete and negatively impacting freshwater biodiversity and contributing to the poor ecological status of rivers. The AMBER Barrier Atlas provides the push we need to take action, and make the removal of obsolete barriers happen everywhere,” says Herman Wanningen, managing director of the World Fish Migration Foundation.

A large dam on the Soča River, in the Slovenian Alps. The Balkan region is home to some of Europe’s last unfragmented river systems. Image: Jan Pirnat | AMBER

The research team state that there are still relatively unfragmented river systems to be found in the Balkans, the Baltic states, and parts of Scandinavia and southern Europe. However, many of these systems are threatened by proposed dam developments. The authors suggest that their results can inform the implementation of the EU Biodiversity Strategy, which aims to restore fragmented river systems across Europe.

“Many barriers are obsolete and removing them provides unprecedented opportunities for restoration,” says Carlos de Garcia de Leaniz, AMBER coordinator and Chair in Aquatic Biosciences at Swansea University. “Our results feed directly into the new EU Biodiversity Strategy and will help to reconnect at least 25,000 km of Europe’s rivers by 2030.”

The new AMBER barrier atlas is a highly valuable resource for environmental managers and policy makers in Europe seeking to underpin their conservation and restoration work with accurate data. An important next step may be to extend and join up this study’s approach to global river systems, particularly where datasets on river barriers are currently restricted.


Belletti, B., Garcia de Leaniz, C., Jones, J. et al. (2020) More than one million barriers fragment Europe’s rivers. Nature 588, 436–441.

Experts urge action to protect and restore small English freshwater habitats

December 3, 2020
Whitchurch Pond. Scientists are increasingly showing the importance of such small water bodies to landscape biodiversity and ecosystem services. Image: Freshwater Habitats Trust

A group of freshwater experts have written to the UK government to call for urgent action to protect England’s small aquatic habitats. They state that the country’s network of ponds, streams, ditches and headwaters – which make up around 80% of England’s freshwaters, and support over 70% of freshwater species – are vital biodiversity hotspots, often providing crucial refuges for rare plants and animals.

However, small freshwater sites are largely ignored by biodiversity monitoring programmes, such as those guided by the EU Water Framework Directive. Linked to this, funding for their protection and restoration is scarce. In short, the authors of the new letter – coordinated by the Freshwater Habitats Trust – argue that there is a critical lack of attention afforded to small freshwaters, and an urgent need to address this blindspot in environmental management and policy.

The open letter is addressed to Dieter Helm, the Independent Chair of the UK government’s Natural Capital Committee, which recently published its final response to the government’s 25 Year Environment Plan. The report explores how the government could address declines in ‘natural assets’ – atmosphere, freshwater, minerals and resources, marine, soils, biota and land – in England over the next quarter century.

The freshwater section of the report identifies small water bodies as a focus of urgent attention. It states that, “The government should develop a baseline and metrics for the condition and extent of smaller waterbodies comparable to those for WFD water bodies. Such an assessment should look to incorporate citizen science to engage communities, and the use of other developing monitoring approaches.”

A number of recent studies have shown that the conservation and restoration of small water bodies can bring about significant environmental benefits. A study by Penny Williams and colleagues published earlier this year found that creating ‘clean water’ pond habitats in farmland can significantly improve landscape biodiversity over relatively short time periods.

A 2018 review by William Riley and colleagues found that small water bodies provide a range of important ecosystem services, such as natural flood control, but are inherently vulnerable to human pressures. A 2016 study by Matthew Hill and colleagues showed that ponds are important ‘stepping stone’ habitats for biodiversity across wide landscapes. And more studies are being published each year, representing a shift in contemporary ecological thought from ‘big is better’ to ‘small is beautiful’ in understanding how freshwater habitats support biodiversity and provide ecosystem services.

In this context, the open letter – signed by 21 prominent UK freshwater researchers – argues that post-Brexit policy change provides an opportunity for the government to address historic shortcomings in the monitoring and protection of small water bodies.

Signatory Dr Jeremy Biggs says, “This could be a win-win solution – for a fraction of what the government and water industry is spending now, we can reverse the inexorable decline of UK freshwater wildlife by focusing on small waters. And post-Brexit changes in legislation give an opportunity to set our own rules to protect freshwater by properly including small waters.”

The letter outlines three key steps for the UK Office for Environmental Protection and other government agencies to address. First, it calls for the implementation of a national monitoring programme for small water bodies which connects with the current river and lake monitoring programmes. Second, it asks policy makers to set specific targets for small waterbody quality and numbers, and integrate these into existing planning and agri-environment policies, such as the Environment Act. Third, it urges the adoption of the Wildlife and Countryside Link recommendations for a funded programme of small water conservation, restoration and creation as part of the next government Spending Review.

In short, the open letter asks the UK government to follow the recommendations of current freshwater research on small water bodies synthesised in the 25 Year Environment Plan report. In doing so, the letter authors argue we can grasp an important opportunity to better monitor, protect and restore vital English ponds, streams, ditches and headwaters in the future.

Pet flea treatments cause toxic chemical pollution in English rivers

November 17, 2020
Image: Nathan Rupert | Flickr Creative Commons

Toxic pesticides found in veterinary flea treatments used on domestic cats and dogs have been detected at potentially harmful levels in English rivers. Researchers have found widespread contamination of two neurotoxic chemicals – fipronil and the neonicotinoid imidacloprid – in 20 sampled rivers, from the Test on the south coast to the Eden in Cumbria. Fipronil was found in 98% of samples, and the average level of its highly toxic breakdown product fipronil sulfone was 38 times above the recommended environmental safety limit.

Both fipronil and imidacloprid are banned for agricultural use due to their harmful environmental effects, including significant reductions in populations of both aquatic and pollinating insects and disruptions to the food webs that depend on them. However, there has been little attention given to the environmental impacts of their use in veterinary flea treatments for cats and dogs. The researchers behind the new study, published in the journal Science of the Total Environment, aimed to address this shortfall by analysing river water samples collected by the Environment Agency between 2016 and 2018.

“The use of pet parasite products has increased over the years, with millions of dogs and cats now being routinely treated multiple times per year,” said lead author Rosemary Perkins, a PhD researcher at the University of Sussex, and a qualified vet. “Fipronil is one of the most commonly used flea products, and recent studies have shown that it degrades to compounds that are more persistent in the environment, and more toxic to most insects, than fipronil itself. Our results, showing that fipronil and its toxic breakdown products are present in nearly all of the freshwater samples tested, are extremely concerning.”

There are 66 licensed veterinary flea treatment products containing fipronil and 21 containing imidacloprid available in the UK. There are around 10 million dogs and 11 million cats in the UK, and the new study suggests that the widespread use of routine flea treatment products has the potential to significantly affect the health of aquatic life in English freshwaters.

“Fipronil and imidacloprid are both highly toxic to all insects and other aquatic invertebrates,” said co-author Professor Dave Goulson from the University of Sussex. “Studies have shown both pesticides to be associated with declines in the abundance of aquatic invertebrate communities. The finding that our rivers are routinely and chronically contaminated with both of these chemicals and mixtures of their toxic breakdown products is deeply troubling.” Speaking to The Guardian, Professor Goulson added that one imidacloprid-based flea treatment for a medium-sized dog contains enough pesticide to kill 60 million bees.

The researchers found that the highest levels of pollution were found immediately downstream of wastewater treatment works. They suggest that this supports the hypothesis that significant quantities of environmentally-harmful pesticides are entering rivers via the washing of treated pets, their bedding, and other surfaces they come into contact with. It is also possible that swimming and rainfall wash-off from treated pets could be additional pathways for the flea treatment pesticides to reach waterways.

“We’ve identified a number of steps that can be taken to minimise or avoid environmental harm from pet flea and / or tick treatments,” outlined Rosemary Perkins. “These range from introducing stricter prescription-only regulations, to considering a more judicious and risk-based approach to the control of parasites in pets, for example by moving away from blanket year-round prophylactic use. We’d recommend a re-evaluation of the environmental risks posed by pet parasite products, and a reappraisal of the risk assessments that these products undergo prior to regulatory approval.”


Perkins R, et al (2020), “Potential role of veterinary flea products in widespread pesticide contamination of English rivers”, Science of The Total Environment,