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

Removing Barriers for Healthy Rivers and Fisheries

World Fish Migration Day brings attention to the connection between fish, rivers and people.

Here's the challenge: Free-flowing rivers around the world are disappearing, putting migratory fish species at risk of extinction and threatening the natural and human communities that depend on them.

Man-made dams, roads, and other barriers prevent migratory fish from reaching their feeding and breeding habitats, while the stagnant water in reservoirs behind dams become deadly hot tubs for many fish species. Climate change and habitat destruction amplify the threat, leading to the disappearance of even more fish species. 

Migratory Fish and Barriers by the Numbers

  • Icon of a waterway.


    Monitored populations of migratory freshwater fish have declined an average of 76 percent between 1970 and 2016.

  • 1/3

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

  • 40%

    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.

  • 2M

    More than 2 million dams, culverts and other barriers across the United States block fish from migrating upstream.

When these barriers challenge the world's migratory fish, the impacts are wide-ranging for people and nature. Migratory fish are an essential part of nature’s food chain, feeding eagles, otters, seals, and other fish and wildlife as they move along rivers and oceans. They play an important role in the cultures and lives of many Indigenous communities, serving as sources of food, trade, wealth, and spirituality. 

And migratory fish support commercial and recreational fishing industries that generate tens of billions of dollars 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. No place on Earth produces more wild salmon than the freshwater lakes and streams of Bristol Bay. The annual returns of wild sockeye salmon number in the tens of millions—a record 66 million sockeye salmon in 2021—and 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.

We can take action now to save migratory fish and restore healthy rivers

The Nature Conservancy is working with communities, businesses, and governments around the world to keep migratory fish – and the rivers and coastal areas they call home – healthy and strong for future generations. 

2022 marks the 20th anniversary of the Sustainable Rivers Program, a partnership between The Nature Conservancy and the US Army Corps of Engineers that improves how dams and other river infrastructure are operated in order to meet the energy and water needs of communities while keeping rivers healthy for migratory fish and other species. 

The decline of migratory fish populations in North America is significantly more pronounced in Europe, Latin America, and the Caribbean, suggesting that sustainable management of fisheries can keep fish populations strong.

AN EPIC JOURNEY: The Great Migration of the Dorado The documentary follows the migration of the Dorado Catfish throughout the Amazon Basin and highlights its relationship with the river, the communities, the forests, and more. See the importance of free-flowing rivers and the urgency for increased freshwater conservation in the Amazon.

In 1999, history was made as efforts began to remove the Edwards Dam on the Kennebec River in Augusta, Maine. The removal marked the first time the federal government determined the public benefits of a free-flowing river were greater than those provided by an existing dam. Making this success possible was the work of many partners, including The Nature Conservancy, Natural Resources Council of Maine, American Rivers, Atlantic Salmon Federation, Trout Unlimited and many others.

Today, iconic and important fish species that were once threatened or had altogether disappeared upstream—species like American shad, Atlantic and short-nosed sturgeon, Atlantic salmon, striped bass, American eel and river herring—are once again found in abundance here for the first time since the Edwards Dam was built in 1837.

Restoration of fisheries continues, not only on Maine's Kennebec and Penobscot rivers, but on rivers across the world.

Why Remove Obsolete Dams?

The removal of dams restores the natural flows and conditions of rivers, as well as the benefits they provide. Obsolete dams can have a wide range of impacts on the environment and local communities, including loss of biodiversity, blocking fish migrations, trapping sediment and nutrients that maintain habitat and estuary health, and altering flow patterns that drive the productivity of downstream floodplains and wetlands. These impacts can affect public safety, food and water supplies, livelihoods, recreation and overall community well-being.

  • Removing obsolete or derelict dams gives rivers more access to natural features—like floodplains, wetlands, side channels and marshes—which can help: improve water quality; support healthier, native plant communities; enhance fish and wildlife habitat; create or enhance recreational opportunities; recharge important aquifers; and, in cases, reduce flood risks for communities. 
  • In the United States, less than 2% of our rivers are free-flowing, contained and diverted by millions of dams, ditches and road crossings and thousands of miles of levees.
  • There are more than 90,000 dams in the U.S. National Inventory of Dams, and—on average—their age exceeds 55 years. However, it’s estimated there are closer to 2 million dams when counting smaller ones not included in the inventory.
  • In its 2017 Infrastructure Report Card, the American Society of Engineers (ASCE) gave dams a “D” rating, noting that “due to the lack of investment, the number of deficient high-hazard potential dams has also climbed to an estimated 2,170 or more. It is estimated that it will require an investment of nearly $45 billion to repair aging, yet critical, high-hazard dams.” 
  • Since 1850, there have been more than 60 dam failures in the United States that have resulted in fatalities. (Source).
  • In Europe, there are 3,000 new dam projects planned for some of the continent's most biodiverse and free-flowing rivers.
A TNC high school intern paddles a canoe on the green river with a rocky outcrop on the riverbank behind her.
GOING WITH THE FLOW A dam removal on Kentucky’s Green River restored more natural flows, which benefits fish and wildlife and enhances recreational opportunities. © 2013 Joanna B Pinneo

Our Related Work

The Conservancy works with leaders in governments, financial institutions, companies, communities and NGOs to remove obsolete dams and other stream barriers. Across the nation the Conservancy has played a direct role in restoring thousands of river miles through the removal of barriers, including dams and poorly designed culverts.  To enable the restoration of tens of thousands more, we’re developing innovative and science-driven ways to finance, prioritize and streamline projects. 

The Conservancy’s related work includes:

Read an article about unleashing New England's rivers from The Nature Conservancy’s magazine.

Broader steps the Conservancy is taking related to dams and river health include

  • The Sustainable Rivers Program. It’s not always feasible or smart to remove dams. The Conservancy and the U.S. Army Corps of Engineers have partnered to improve the way some of the Corps dams are operated to produce more benefits and minimize environmental impacts.
  • Developing Science to Guide Investments. With more than 2 million dams in the United States, the Conservancy is helping to lead the way to identify where to make restoration investments that maximize benefits to people and nature. 
  • Financing Innovations. The U.S. Army Corps of Engineers, which owns and operates most of the nation’s largest dams, recently announced that dam removals can be used to mitigate the development of streams, making millions of dollars per year available for this river restoration tool. This regulatory shift was founded in research conducted by the Conservancy.
  • Streamlining the regulatory processes for the redesign, re-operation or removal of dams.
  • Expanding regional prioritization approaches to better understand the ecological ‘return on investment’ when selecting dam removal projects.
  • Developing training materials for Nature Conservancy and partner staff to advance a large number of cost-effective dam removal projects.
  • Identifying private and innovative funding approaches to match limited federal and state funds for dam removal projects.
  • Using lessons learned in the United States to influence the siting of dams and their operations around the globe. Learn more.