Global Freshwater Fish Migrations Face Catastrophic Collapse
A comprehensive new global assessment has revealed that vital freshwater fish migrations are collapsing worldwide at an alarming rate. The study, led by biologist Zeb Hogan for the March 2026 meeting of parties to the Convention on the Conservation of Migratory Species of Wild Animals, provides the clearest picture yet of this devastating decline.
The Silent Suffering Beneath the Surface
Hidden beneath the world's river surfaces, extraordinary animal movements once unfolded with seasonal predictability. For centuries, migrations of salmon, sturgeon, giant catfish and numerous other species moved through rivers in vast numbers, their biomass rivaling the famous mass movements of zebra and wildebeest across the Serengeti.
These migratory species represent extraordinary diversity, ranging from beluga sturgeon – massive fish that can live over a century and produce the world's most prized caviar – to giant river carp, tropical eels, gold-flecked shad and goliath catfish. Their survival depends on journeys that can span hundreds or even thousands of miles, with some migrations crossing entire continents.
Alarming Statistics Reveal Critical Situation
The research team reviewed more than 15,000 species of freshwater fish, identifying which migrate and assessing their conservation status. The results are sobering: researchers identified 325 migratory freshwater fish species as candidates for coordinated international conservation actions under the Convention on Migratory Species treaty.
Among migratory fish already listed under the Convention on Migratory Species, 97% are at risk of extinction. In Asia, populations of migratory freshwater megafish have declined by over 95% since 1970. Many of the largest species, the giants that make the longest and most dramatic journeys, are in the most serious trouble.
Why Migratory Fish Are Struggling
For most migratory fish, movement is not optional – it is essential for survival. When dams block routes, when fishing intensifies at migratory bottlenecks, and when floodplains and spawning grounds are cut off or degraded, these fish cannot simply relocate. First the migration thins, then it falters, and in rivers blocked by dams, it disappears completely.
Migratory freshwater fish depend on long, connected river corridors that often span multiple countries. Dams, habitat fragmentation, pollution, overfishing and climate-driven changes are systematically breaking these connections. Once routes are severed, populations can collapse with frightening speed.
Global Hotspots of Concern
The disappearing giants of the Mekong River illustrate the crisis. The Mekong giant catfish, which grows to more than 650 pounds and once migrated hundreds of miles along the river, is now critically endangered. Dams block its route to spawning grounds while overfishing at migration bottlenecks kills the large adults that populations depend on.
In Cambodia, small migratory fish known as trey riel are so significant they gave their name to the national currency. In South Asia, the migratory hilsa shad holds such cultural importance that it is sometimes given as a wedding gift, wrapped in ornate cloth and adorned with flowers.
Declines are unfolding across other great river systems:
- In the Amazon, the dorado (gilded catfish) completes migrations of more than 6,000 miles between Andean headwaters and coastal nurseries – the longest freshwater fish migration ever recorded. Altered river flows, barriers and overfishing are increasingly disrupting these journeys.
- Across the Northern Hemisphere, migratory fish such as salmon, sturgeon and shad have suffered major losses as rivers have been dammed and polluted while populations were heavily overfished.
- In South Asia, fish including mahseer, goonch catfish and hilsa are declining under pressure from dams, overharvesting, sand mining, pollution and habitat loss.
The International Dimension of the Crisis
This is fundamentally an international problem. More than 250 rivers and lakes worldwide cross national borders, and approximately 47% of Earth's land surface lies within shared river basins. Yet freshwater fish are still too often managed at local or national scales, as if rivers and fish movements stop at political boundaries.
The Convention on Migratory Species represents the only global treaty specifically designed to encourage countries to work together to conserve migratory animals. For freshwater fish, cooperation can begin with countries sharing data and extend to coordinated actions to reduce overharvesting, protect floodplains and spawning grounds, and maintain river connectivity.
Pathways to Recovery
Restoring migratory fish populations requires multiple approaches:
- Keeping healthy rivers free-flowing
- Reconnecting rivers fragmented by dams and channelization
- Improving fisheries management
- Protecting floodplains and wetlands
- Restoring habitats that have been drained, cleared or isolated by development
There are examples of success. In Washington state, dam removals on the Elwha and White Salmon rivers reopened habitat that had been inaccessible for migrating fish for about a century, allowing Chinook, coho, steelhead and lamprey to return.
The river basins where international cooperation is now most urgently needed include the Amazon and La Plata-Paraná in South America, the Danube in Europe, the Mekong in Asia, the Nile in Africa and the Ganges-Brahmaputra in South Asia.
The world's great fish migrations have not disappeared everywhere, but they are fading rapidly. This new assessment offers a clearer picture of where international cooperation is most urgently needed to protect these extraordinary aquatic animals that support millions of people, enrich human cultures, and make our world a more wondrous place.
