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Just One-Third of the Longest Rivers Still Free-Flowing

The first ever global assessment of the location and extent of the planet’s remaining free-flowing rivers highlights severe degradation, and offers a method for tracking the status of free-flowing rivers over time.

This echoes the assessment of the river basin management plan for the Danube catchment of 2015. At that time, the International Commission for the Protection of the Danube River had identified 1030 continuity interruptions such as hydropower dams on rivers with catchments larger than 4000 km2 in the Danube region; 50% of which related to hydropower use. Moreover, two-thirds of all dam-like structures are without fish migration. While the impact on fish and other freshwater organisms is enormous, these figures even exclude a large number of small hydropower plants whose impact also adds up, while more hydropower dams are in the planning stage.

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Globally, just over one-third (37%) of the world’s 246 longest rivers remain free-flowing, according to a new study published yesterday in the scientific journal Nature. Dams and reservoirs are drastically reducing the diverse benefits that healthy rivers provide to people and nature across the globe.

A team of 34 international researchers from McGill University, WWF, and other institutions[i] assessed the connectivity status of 12 million kilometres of rivers worldwide, providing the first ever global assessment of the location and extent of the planet’s remaining free-flowing rivers[ii].

Among other findings in ‘Mapping the World’s Free-Flowing Rivers,’ the researchers determined only 21 of the world's 91 rivers longer than 1,000 km that originally flowed to the ocean still retain a direct connection from source to sea and are largely restricted to remote regions of the Arctic, the Amazon Basin and the Congo Basin. In Central and Eastern Europe, the Danube’s flow is being impeded by the Iron Gates Dams at river kilometre 863, hindering highly threatened migratory sturgeons and other fish from entering important spawning and feeding sites in the Middle Danube.

“The world’s rivers form an intricate network with vital links to land, groundwater, and the atmosphere,’’ said lead author Günther Grill of McGill’s Department of Geography. ‘’Free-flowing rivers are important for humans and the environment alike, yet economic development around the world is making them increasingly rare. Using satellite imagery and other data, our study examines the extent of these rivers in more detail than ever before.”

Dams and reservoirs are the leading contributors to connectivity loss in global rivers. The study estimates there are around 60,000 large dams worldwide, and more than 3,700 hydropower dams are currently planned or under construction. They are often planned and built at the individual project level, making it difficult to assess their real impacts across an entire basin or region.

“This first ever map allows us to prioritise and protect the world’s remaining free-flowing rivers, as these are lifelines for wildlife and people across the globe,” said Michele Thieme, WWF Freshwater Scientist and co-author of the paper. “Rivers provide diverse benefits that are often overlooked and undervalued. Decision-makers must consider the full value of rivers when they plan new infrastructure.”

Healthy rivers support freshwater fish stocks that improve food security for hundreds of millions of people, deliver sediment that keeps deltas above rising seas, mitigate the impact of extreme floods and droughts, prevent loss of infrastructure and fields to erosion, and support a wealth of biodiversity. Disrupting rivers’ connectivity often diminishes or even eliminates these critical ecosystem services.

Protecting remaining free-flowing rivers is also crucial to saving biodiversity in freshwater systems. WWF’s Living Planet Report 2018 recently revealed that populations of freshwater species have experienced the most pronounced decline of all vertebrates over the past half-century, falling on average 83 percent since 1970. This week, Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services’ (IPBES) 2019 Global Assessment Report on Biodiversity and Ecosystem Services highlighted threats to the world’s freshwater ecosystems and called for the protection and restoration of free-flowing rivers.

The study also notes that climate change will further threaten the health of rivers worldwide. Rising temperatures are already impacting flow patterns, water quality, and biodiversity. Meanwhile, as countries around the world shift to low-carbon economies, hydropower planning and development is accelerating, adding urgency to the need to develop energy systems that minimise overall environmental and social impact.

“While hydropower inevitably has a role to play in the renewable energy landscape, countries should also consider other renewable options,” said Thieme. “Well-planned wind and solar energy can have less detrimental impacts on rivers and the communities, cities, and biodiversity that rely on them.”

With the historic coming together of key decisions on environment, climate and sustainable development, 2020 provides an unmissable opportunity for world leaders to protect and restore free flowing rivers as part of a New Deal for Nature and Peoplean agreement which would aim to halt and reverse the loss of nature, and protect our planet.

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