On this International Day for Action for Rivers, we recognise rivers as the vital arteries of our planet. Rivers are the lifelines of our planet, supporting extraordinary biodiversity and providing water, food, and other ecosystem services to billions of people. Yet freshwater ecosystems are among the most imperiled. Global populations of freshwater species have plummeted 83% on average since 1970 – a far sharper decline than in terrestrial or marine realms. Pollution, dam construction, over-extraction, and climate change have pushed many rivers to ecological crisis. Below, we examine major rivers’ challenges, highlight successful restoration case studies, present key scientific statistics on biodiversity loss, pollution and climate impacts, review emerging conservation technologies, and give examples of international collaboration in safeguarding rivers.
Major Rivers and Their Ecological Challenges
The Amazon River (South America)
The Amazon River in South America, Peru, South America.
The Amazon River system – the world’s largest – boasts unparalleled biodiversity, harboring about 13% of all known freshwater fish species on Earth along with countless other aquatic and terrestrial organisms. However, the Amazon is under severe threat. Deforestation in the basin (17% of Amazon forests have been lost, with another 17% degraded) is altering rainfall patterns and adding sediment to waterways. Dozens of hydroelectric dams are planned or built on Amazon tributaries, fragmenting rivers and imperiling migratory fish and aquatic mammals like the pink river dolphin. The region also faces an invisible pollution crisis: mercury used in illegal gold mining is contaminating rivers. A WWF report found mercury pollution has already affected the health of over 1.5 million people in the Amazon basin, poisoning fish and iconic predators such as river dolphins and jaguars. These impacts, compounded by climate change (e.g. more frequent extreme droughts), pose grave risks to the Amazon’s unique riverine ecology.
Yangtze River (China)
Tiger Leaping Gorge, Yangtze river, Lijiang City, Yunnan Province China.
The Yangtze, Asia’s longest river (6,300 km), sustains remarkably rich wildlife – over 350 fish species and hundreds of amphibians, reptiles, birds, and mammals live in its basin. However, decades of rapid economic growth have taken a heavy toll. Industrial and agricultural pollution has multiplied, filling the Yangtze with untreated waste, animal manure, and chemicals. At the same time, massive hydrological engineering has altered the river: more than 50,000 dams have been built in the Yangtze basin since 1950. This fragmentation of the river’s flow has devastated aquatic life – most famously, the Yangtze river dolphin (Lipotes vexillifer) was declared functionally extinct after 2006, a high-profile casualty of pollution and overfishing. Another giant endemic, the Chinese paddlefish, was recently confirmed extinct as well; a main cause was a dam that blocked its migration route. These losses underscore the Yangtze’s ecological crisis. In response, China has launched initiatives like a 10-year fishing ban (2020–2030) on the Yangtze to help depleted fish populations recover, and large investments are being made to improve wastewater treatment. But the river’s health remains in precarious balance, also threatened by climate-related droughts and flooding swings.
Mississippi River (United States)
Mississippi River with Minneapolis beyond.
The Mississippi River drains 41% of the contiguous U.S., making it a major hub for agriculture and industry. However, fertilizer and manure runoff from Midwest farms have led to chronic nutrient pollution. More than half of the river miles in its basin have unsafe nitrogen and phosphorus levels. Each summer, this pollution fuels a massive Gulf of Mexico "dead zone"—averaging 5,000–6,000 square miles—where aquatic life cannot survive. Beyond pollution, the river’s ecology has been heavily engineered. Levees and channelization have disconnected it from floodplain wetlands, with Missouri losing 87% of its original wetlands to land conversion and flood control. This reduces habitat, weakens natural water filtration, and worsens flooding. Climate change compounds these issues, with heavier rainstorms increasing runoff and warming temperatures degrading water quality. While efforts like nutrient management and wetland restoration are underway, the Mississippi remains a prime example of a river under intense environmental pressure.
Global Trends: Biodiversity Loss, Pollution, and Climate Impacts
Global assessments underline several critical trends affecting rivers worldwide:
Freshwater Biodiversity in Crisis
Populations of mammals, birds, amphibians, fish, and other freshwater-dependent species have declined more than 80% since 1970 – the steepest drop of any biome. Habitat loss, damming, invasive species, overfishing, and pollution have driven roughly one in four freshwater species to risk of extinction. For instance, nearly a third of freshwater fish species are now threatened globally. This biodiversity free-fall has huge implications, as rivers support immense food webs and provide protein for hundreds of millions of people.
Widespread River Pollution
Water quality is a major concern in most river basins. About 80% of the world’s wastewater is released into the environment without adequate treatment, meaning rivers often serve as dumping channels for raw sewage, industrial effluents, and agricultural runoff. The result is rampant pollution – from toxic chemicals and heavy metals to excess nutrients and microplastics – degrading freshwater habitats. For example, high nutrient levels have caused algal blooms and oxygen-depleted “dead zones” not only at the Mississippi’s mouth, but in dozens of river estuaries globally. In Asia, rapid urbanisation means many major rivers (Ganges, Yangtze, etc.) suffer severe bacterial contamination and periodic fish kills. Even in developed regions, over half of rivers fail to meet basic water quality or ecological health criteria due to legacy pollution and runoff.
Industrial waste water discharge pipes.
Climate Change Impacts
Global warming is intensifying hydrological extremes and thermal stress in rivers. Heavier downpours are already causing more frequent and severe river floods in many regions, while prolonged droughts are shrinking flows elsewhere. These shifts directly threaten riverine life. A stark example occurred in 2023 in the Amazon: a severe drought dropped river levels and water in lagoons soared to 39 °C (over 102 °F), about 10 °C above normal. The result was a mass die-off – 120 endangered Amazon river dolphins were found dead in one week, along with thousands of fish, due to overheating and oxygen depletion. Such events, once extremely rare, may become more common as climates warm. Moreover, the retreat of glaciers is reducing dry-season flows in glacier-fed rivers (affecting water supply for millions), and warming rivers can disrupt fish spawning and increase invasive species. In sum, climate change multiplies existing stresses, making river conservation an even more urgent challenge.
A dead Amazon dolphin at confluence of Tefe Lake and the Solimoes River in Tefe, Amazonas state, Brazil, on October 1, 2023. Credit: Bruno Kelly/Reuters.
Success Stories: River Restoration and Conservation Initiatives
Despite the challenges, there are inspiring examples of rivers rebounding when given a chance. Several river restoration projects and conservation initiatives demonstrate that degraded rivers can recover:
Rhine River (Europe)
Once nicknamed the “sewer of Europe” in the 1960s due to extreme pollution, the Rhine has transformed into one of the cleanest international rivers through decades of cooperation and investment. The multinational Rhine Action Programme (launched 1987) led to over €80 billion invested in wastewater treatment, cutting inputs of many pollutants by 70–100%. Water quality improved dramatically, and migratory fish have returned – by 2012, nearly 7,000 Atlantic salmon were recorded ascending the Rhine to spawn once again (after being absent for decades). This revival earned the Rhine the first-ever European RiverPrize for outstanding restoration. It showcases how bold targets (like “Salmon 2000”) and international collaboration can restore a river’s health.
River Thames (United Kingdom)
The Thames flowing through London was declared “biologically dead” in 1957 due to oxygen depletion and pollution. Since then, major investments in sewage treatment and tighter water quality standards have revived the Thames. By 2021 scientists documented 115 fish species in the river, and surprising fauna like seahorses, seals, and even small sharks now inhabit its tidal reaches. Bird and marine mammal populations show positive trends as well. While challenges remain (e.g. combined sewer overflows during storms), the Thames’ recovery from ecological ruin to a living river in a few decades stands as a model urban river restoration, largely credited to strong environmental regulations and continuous monitoring.
View of Elizabeth Tower, Houses of Parliament and Thames river, London, United Kingdom.
The Elwha River restoration in Washington State
This is one of the world’s largest river recovery projects. Two dams, built in the early 1900s, blocked salmon from 90% of their habitat, causing populations to collapse. Between 2011 and 2014, both dams were removed—the largest dam removal project to date—reopening 70 miles of habitat. Nature responded immediately. In the first year, over 4,000 Chinook salmon spawned above the former dam site for the first time in a century. By 2014, 32,000 coho salmon fry emerged from areas once buried under reservoirs. Other species, including steelhead trout and lamprey, also returned. With the dams gone, 33 million tons of sediment washed downstream, rebuilding the estuary and creating 70 acres of new wetlands. These revitalised mudflats now support shellfish, insects, and forage fish, benefiting birds and marine life. While full salmon recovery (historically 400,000 per year) will take time, this project proves how dam removal can rapidly restore ecosystems—inspiring similar efforts worldwide.
Glines Canyon Dam on the Elwha River in Washington State, during demolition activities in 2011. Credit: John Gussman.
Many other examples could be noted: the Danube River in Europe, where international efforts have reduced pollution and restored wetlands; Japan’s Kanda River, daylighted and cleaned in Tokyo; or estuaries like Chesapeake Bay, where nutrient controls are slowly improving water quality. Each success story reinforces that with political will, funding, and science-based action, even heavily degraded rivers can be brought back to life.
International Collaboration for River Conservation
Because rivers often cross political boundaries, international cooperation is crucial to conserve and restore them. Encouragingly, there are several frameworks and organisations uniting countries for river stewardship:
Mekong River Commission (MRC)
The Mekong River flows through six Southeast Asian countries, making regional cooperation essential. Established in 1995, the Mekong River Commission (MRC) facilitates joint management of the Lower Mekong Basin, with Cambodia, Laos, Thailand, and Vietnam as full members, while China and Myanmar cooperate as partners. The MRC focuses on data sharing, flood warning systems, fisheries research, and sustainable basin planning, aiming to balance hydropower development with ecological protection. It conducts annual fish stock surveys and provides guidelines for dam projects, including fish passage systems. Although challenges remain—such as the absence of full upstream participation—the MRC serves as a neutral platform for negotiations on water releases, sediment loss, and drought impacts.
Nile Basin Initiative (NBI)
Aerial view of the White Nile River, Juba, South Sudan.
The Nile River, the world’s longest, is shared by 11 African nations. In 1999, these countries formed the Nile Basin Initiative (NBI) to foster basin-wide cooperation and sustainable water management. The NBI unites Egypt and Sudan with upstream nations like Rwanda and Uganda, ensuring that water allocation and dam projects are managed collectively for mutual benefit. Key projects include the Nile Equatorial Lakes hydromet system, improving river monitoring, and watershed restoration programs in the Blue Nile and Lake Victoria sub-basins. Though a formal treaty (Cooperative Framework Agreement) remains under negotiation, the NBI has successfully built trust and cooperation, leading to new irrigation infrastructure and environmental impact assessments.
Amazon Cooperation Treaty Organisation (ACTO)
Signed in 1978 and formalised in 1995, the Amazon Cooperation Treaty unites eight Amazon Basin countries—including Brazil, Peru, Colombia, and Bolivia—to promote sustainable development and conservation. The Amazon Cooperation Treaty Organisation (ACTO) oversees initiatives to combat illegal wildlife trade, protect forests, and improve hydrological data sharing. ACTO’s Strategic Action Program helps countries identify pollution hotspots and preserve critical wetlands. Additionally, ACTO engages indigenous communities and scientific networks in conservation efforts. While coordinating across the vast Amazon Basin is complex, ACTO remains a crucial platform for transboundary cooperation, recognising that Amazonian rivers and rainforests are deeply interconnected across national borders.
International collaboration isn’t limited to these examples. Europe has robust transboundary frameworks under the EU Water Framework Directive – for instance, the International Commission for the Protection of the Danube River (ICPDR) coordinates 14 countries (and the EU) in reducing Danube pollution and improving habitat connectivity. Likewise, the Rhine’s cleanup was driven by a commission uniting countries from Switzerland to the Netherlands. In Southern Africa, countries cooperate on the Limpopo and Okavango rivers, and in North America the US and Canada jointly manage boundary waters (e.g. Great Lakes and Columbia River) through treaties. These collaborations show that rivers can be a source of cooperation rather than conflict.
By sharing data, aligning policies, and undertaking joint conservation projects, nations can more effectively tackle issues like pollution control, flood management, and species protection at the river-basin scale.
As global recognition of this approach grows, cooperative management continues to solidify its role as a fundamental element of successful river conservation efforts worldwide, underscoring the undeniable importance of unity in safeguarding our planet's vital waterways.
