MIGRATORY FISH. Herring and other fish migrate across the globe. ©: Eric Aldrich / TNC
Underwater video of herring migrating upstream.
Fish Migration In spring, herring migrate up the Nemasket River in Middleboro, Massachusetts. © Eric Aldrich / TNC

Climate Change Stories

Water Connects Us All—Fish Included

The connection between fish and people.

Each year, more than 1,000 fish species around the world migrate to, from or within rivers to reproduce, escape predation or drought, find feeding grounds, seek warmer or cooler waters, or fulfill other critical life cycle needs. Healthy river and stream corridors are also essential for amphibians, reptiles and mammals, such as manatees and river porpoises. Some swim from larger rivers, lakes or headwaters, while others—like salmon, river herring and some trout—travel thousands of miles across oceans and bays to reach critical freshwater habitats. Sadly, their journeys are increasingly becoming more treacherous, or not possible at all.

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These aquatic species face obstacles of all sorts, such as dams, locks, levees and culverts, many of which are impassible. Sometimes the places they need to get to—floodplains, wetlands and side channels that offer life-stage-specific nutrition, protection from predators and ideal conditions for rearing young or laying eggs—have been destroyed or are severely degraded. We know that wetlands are disappearing at three times the rate of tropical forests, and, according to new research in Scientific Data, in just the last 30 years, we've lost nearly 232,000 square miles (600,000 square kilometers) of floodplains—an area the size of France or California.

And the same waters through which fish migrate or go to spawn are becoming increasingly polluted, or in some cases, drying up all together.

These are the primary reasons why freshwater species populations around the globe have declined an average of 81% since 1970—far more than declines seen in terrestrial or marine species.

Migratory Fish and Barriers by the Numbers

  • Blue icon of a fish.


    Monitored populations of migratory freshwater fish have declined an average of 81% between 1970 and 2020.

  •  Blue icon of a river flowing next to a tree.


    Just one-third of the world's longest rivers remain free-flowing.

  •  Blue icon of water waves.


    River systems altered by dams and other barriers have led to 40% of America’s fish species being listed as imperiled and many commercial fisheries being decimated.

  •  Blue icon of a fish.


    Nearly 1 million dams, culverts and other barriers across the United States block fish from migrating upstream.

Such declines affect more than just fish and other wildlife. Migratory fish support commercial and recreational fishing industries that generate tens of billions in revenue each year. In Alaska’s Bristol Bay alone, the sustainable commercial harvest of wild salmon is valued at $2.2 billion annually and employs more than 10,000 people. In 2022, Bristol Bay experienced a record return of nearly 72 million sockeye salmon. This yearly migration makes for a rich ecosystem and remarkable way of life for people in Indigenous communities where the harvest of wild salmon is a cherished part of their culture.

How We Improve Freshwater Health & Connectivity

We Protect and Restore Freshwater Systems

Fresh water is connected to everything The Nature Conservancy does, and we’re determined to protect and restore freshwater ecosystems at unprecedented scales. By leveraging our long history of innovation and collaboration, we know we can scale up breakthrough strategies for fresh water that are durable and long-lasting. Our work in Ecuador serves as a prime example of ways in which we’re implementing long-term protection efforts to conserve freshwater systems above and below ground to keep them healthy and intact.

We’re already working on close to 400 projects in nearly 40 countries, but we must go further and faster to achieve our goals for 2030. (For a broader picture of our freshwater work around the globe, visit “Water Connects Us All” on nature.org.)

Building Homes for Salmon (4:57) Learn how TNC is restoring streams in northern California to benefit coho salmon, a species that—with just 1% of its historic population—is barely hanging on in the Golden State.

Protection and restoration can go hand-in-hand. TNC’s work to restore streams, rivers, wetlands and floodplains is a strategy we use to mitigate the impacts of man-made structures or development that affect the hydrology and health of freshwater systems and the wildlife and people that depend on them.

Many of these man-made structures, like ditches, levees or dikes, are designed to drain wetlands or straighten rivers by cutting them off from side channels or floodplains, which often provide some of the most important habitat for fish and a wide array of other species. These same structures can drastically impact the trees and plants in these places, which are adapted to periodic, natural fluctuations of high and low flows.

TNC has dozens of projects to improve the health of streams by restoring natural meanders and/or reconnecting them to side channels or other low-lying areas, and we and our partners have spearheaded some of the largest floodplain reconnection projects in the United States. Learn more.

We Overcome Barriers and Ensure Rivers Flow Freely

Only some one-third of the world’s largest rivers remain free flowing. Most have been severed by dams or other barriers. For example, in the United States, only some 2% of the nation’s 3 million miles of rivers and streams remain free-flowing and undeveloped, similar to other heavily developed nations. And countless other, smaller rivers and streams been altered by dams, locks, levees or culverts that impair or prevent the migration of aquatic species.

WHEN RIVERS RETURN (3:45) When rivers are restored, see how life returns and people benefit.

Overcoming Barriers

Below is a snapshot of how TNC addresses barriers that affect our freshwater systems. Click on each square to learn more.

Split view of a school of salmon underwater facing a stream bank in a forest, which is seen above the water line.
Against the flow Many salmon species, like these coho salmon in Washington, spawn in streams fed by cooler springs fed by groundwater. © Adam Baus/TNC Photo Contest 2021

Groundwater Isn’t Just Underground

Did you know that groundwater provides about 30% of the nation’s surface streamflow, according to estimates from the U.S. Geological Survey? The rest is from rain and snowmelt. And some systems are completely driven by groundwater or completely dependent.

Examples of Our Freshwater Work

The projects below are not a complete listing of the projects TNC is involved with to help improve the health of our freshwater systems. Rather, what’s listed below serve as some of our best examples, many of which feature videos.

Select Freshwater Projects

Click on each square to learn more.

Partnerships & Funding that Improve Freshwater

As an environmental non-profit organization, the support of our donors enables TNC to leverage its science-based expertise and past work to influence and implement new projects that improve the health of freshwater systems around the globe. It’s important to note, however, that in the face of so much loss and degradation of habitat, partnerships—and the funding they can provide—are paramount in order to work at scale and achieve meaningful results.

In the U.S., critical partnerships and related funding include, but are not limited to:

  • The National Oceanic and Atmospheric Administration (NOAA)
  • The National Fish Passage Program
  • The U.S. Fish and Wildlife Service
  • The U.S. Forest Service
  • The Natural Resources Conservation Service
  • The Bureau of Indian Affairs
  • Native American Fish and Wildlife Society
  • The Federal Highways Administration
  • The National Fish Habitat Partnership
  • American Rivers
  • The Atlantic Salmon Federation
  • Trout Unlimited
  • Numerous state fish and wildlife agencies
  • Many local U.S. Tribes and Canadian First Nations

Internationally, critical partnerships include, but are not limited to:

  • Dam Removal Europe
  • World Wildlife Fund
  • World Fish Migration Foundation
  • Wetlands International
  • Fauna and Flora International
  • Conservation International