Populations of migratory freshwater fish have collapsed by 81% since 1970, according to the most recent Living Planet Index assessment, a decline steeper than nearly any other wildlife group on Earth. The finding, released ahead of the next Conference of the Parties for the Convention on Migratory Species (CMS COP15), frames a crisis that is largely invisible to the public because it unfolds beneath the surface of rivers, lakes, and floodplains. With nearly half of all migratory animal species now in decline, the freshwater fish numbers represent the sharpest edge of a broader ecological breakdown that threatens food systems and biodiversity across every continent.
An 81% Collapse Hidden Underwater
The Living Planet Index for Migratory Freshwater Fish 2024 Update tracked population trends across species that depend on seasonal movement through freshwater systems to feed, breed, and survive. The 81% decline in freshwater migratory fish dwarfs losses recorded for terrestrial and marine migratory species, making rivers and lakes the most dangerous habitats for animals on the move. Animals inhabiting freshwater ecosystems are declining faster than those in any other biome, a pattern that researchers attribute to the unique vulnerability of river corridors to human infrastructure and pollution.
Some of these fish travel extraordinary distances. Certain species can migrate over 7,000 miles through interconnected waterways, crossing national borders and climate zones. Salmon swimming upstream to spawn on rivers like the Tyne in Northumberland, eels crossing the Atlantic, and giant carp navigating Southeast Asian floodplains all depend on unbroken river connectivity. When that connectivity fails, so do the populations.
Dams, Pollution, and 1.2 Million Barriers
The drivers behind this collapse are well documented but poorly addressed. An estimated 1.2 million barriers such as weirs and dams block fish migrations worldwide, fragmenting habitats that species need to complete their life cycles. Dams do not simply reduce fish numbers gradually; peer-reviewed research published in the Proceedings of the National Academy of Sciences found that dams trigger exponential population declines in migratory fish, meaning losses accelerate rather than stabilize after construction.
Hydropower expansion is intensifying this pressure on some of the planet’s most biodiverse river systems. International rivers undergoing major hydropower development include the Amazon, Congo, and Mekong, three basins that together support thousands of freshwater species and hundreds of millions of people who depend on fish protein. Mining, water abstraction, and chemical pollution compound the damage, degrading water quality and altering flow regimes even in stretches between dams.
What makes this problem especially difficult to solve is that rivers do not respect political boundaries. A dam built in one country can wipe out a fish population that spawns in another. Cooperation between governments sharing a river basin is essential, yet the institutional frameworks for that cooperation remain weak. The Convention on Migratory Species, the primary international treaty designed to protect animals that cross borders, covers only a small share of freshwater migrants, leaving the vast majority of affected species without formal international protection.
Why CMS Protections Fall Short
Most public attention on migratory species focuses on charismatic birds, whales, and large terrestrial mammals. Freshwater fish have been largely overlooked in CMS listings, even though their population losses are the most severe of any migratory group. A peer-reviewed analysis in Nature Reviews Biodiversity examined the governance gaps within CMS and found that the treaty’s existing tools are rarely applied to river systems, despite their clear relevance.
This gap matters because CMS listing triggers specific obligations: signatory nations must work to conserve listed species and their habitats, coordinate with neighboring countries, and reduce threats from infrastructure and pollution. Without listing, there is no binding international framework requiring governments along the Amazon, Congo, or Mekong to jointly manage fish passage, sediment transport, or ecological flows around dams. The result is a patchwork of national regulations, many of which prioritize energy production and short-term economic gains over biodiversity and long-term food security.
Experts argue that CMS could be rapidly strengthened for freshwater fish by adding more species to its appendices and by developing basin-level action plans that treat rivers as connected systems rather than isolated national assets. Such plans could set shared standards for environmental impact assessments, minimum flow requirements, and fish passage technologies, while also integrating indigenous and local knowledge about seasonal migrations.
Regional Crises From Europe to Southeast Asia
The global 81% figure masks even steeper regional losses. Europe’s migratory freshwater fish, including Atlantic salmon and European eel, have suffered some of the longest-running declines, driven by centuries of dam construction, river straightening, and pollution. Even as water quality has improved in some European rivers, the physical barriers that prevent fish from reaching spawning grounds remain in place, limiting recovery.
In Southeast Asia, the giant carp, a critically endangered species, illustrates how quickly things can unravel. Once abundant in the Mekong basin, it has been pushed to the brink by overfishing, dam construction that blocks its migration routes, and the loss of floodplain spawning grounds. Similar stories are playing out for sturgeons in Eastern Europe, catfish in the Amazon, and river herring along the Atlantic coast of North America.
These regional collapses are not just a conservation concern; they are a direct threat to human well-being. In many low-income and rural communities, migratory freshwater fish are a primary source of protein, micronutrients, and income. When fish populations crash, families are forced to turn to more expensive and often less nutritious food sources, and local economies built around seasonal fisheries can disintegrate within a generation.
Pathways to Recovery
Despite the grim statistics, there are proven solutions that can help reverse the decline of migratory freshwater fish. One of the most effective interventions is the removal or modification of obsolete dams and weirs. Across parts of Europe and North America, hundreds of small barriers have been dismantled in recent years, leading to rapid rebounds in some fish populations and the restoration of natural river dynamics.
Where dams are deemed essential for energy or water storage, retrofitting them with effective fish passage systems and adjusting operating rules to mimic natural flow patterns can significantly reduce their impact. Research on ecological operation techniques suggests that more flexible management of reservoirs and turbines can improve survival rates for migrating fish without eliminating hydropower generation.
Protecting and restoring floodplains is another critical piece of the puzzle. Many migratory fish depend on seasonal floods to access spawning and nursery habitats in wetlands and side channels. Levee setbacks, wetland restoration projects, and the reconnection of rivers to their floodplains can all enhance these life-cycle stages while also providing co-benefits such as flood protection and carbon storage.
At the governance level, expanding CMS coverage for freshwater fish would send a powerful signal that these species are a global priority. Basin-wide agreements that align national policies on dam planning, pollution control, and fisheries management could help ensure that conservation gains in one country are not undone by uncoordinated development upstream or downstream.
People, Institutions, and the Future of Rivers
Delivering these changes will require not only political will but also technical expertise and sustained investment. Institutions such as the United Nations University, which recruits specialists in environmental governance and water management through its global career opportunities, are positioned to support countries in designing science-based policies for river basins under pressure.
In Japan, for example, the United Nations University’s presence in Tokyo, highlighted on its Japanese-language portal, has helped connect researchers, policymakers, and civil society organizations working on issues from climate resilience to sustainable fisheries. Similar networks in other regions could foster the cross-border collaboration that migratory freshwater fish so urgently need.
Ultimately, the 81% collapse in migratory freshwater fish populations is a warning that the world’s rivers are approaching a tipping point. Reversing this trend will mean rethinking how societies value and manage freshwater systems, shifting away from a narrow focus on short-term extraction toward a model that recognizes rivers as living infrastructure. If governments can harness international treaties like CMS, invest in river restoration, and listen to the communities that depend on these waters, the next Living Planet Index update could begin to tell a different story, one of recovery, rather than relentless decline.
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*This article was researched with the help of AI, with human editors creating the final content.
