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.
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
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81%
Monitored populations of migratory freshwater fish have declined an average of 81% between 1970 and 2020.
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1/3
Just one-third of the world's longest rivers remain free-flowing.
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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.
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1M
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.)
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.
Overcoming Barriers
Below is a snapshot of how TNC addresses barriers that affect our freshwater systems. Click on each square to learn more.
Removing Obsolete Dams
In cases where the value dams provide is outweighed by operational costs and the impacts to nature and people, TNC supports their removal. The removal of dams restores flows and the benefits they provide to people and nature. 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.
Avoiding New Dams
Or ensuring the “right fit.” More than 161,000 miles (260,000 kilometers) of free-flowing rivers are at risk of being impacted by the construction of new hydropower dams—equal to more than 39 times the length of the Nile. The impacts of these new dams would fall disproportionately in river basins with the greatest freshwater fish harvests and with the highest diversity of freshwater species, and—in many cases—greatly affect critical food sources for or displace Indigenous peoples.
Although dams can provide hydroelectric power, help reduce flood risk and store water to use later to irrigate crops, for drinking water and other purposes, their high ecological and socioeconomic costs mean they must prove their worth, and the case against them in our evolving energy sector is considerable. When and where new dams are proposed, we advocate for large-scale planning that factors in energy demand, other sources of renewable energy, project costs, and environmental and societal impacts. Our work within Brazil’s Tapajos River basin well illustrates this strategy put into action.
A Focus on Culverts
When roads cross streams—often over culverts—it can be problematic for the stream’s health and the safety of the road. Not only can poorly designed or undersized culverts hinder or block the migration of aquatic species, they can fail due to the increasing intensity of storms and growing development, which produces more runoff. TNC works with many partners to identify and fix problematic road crossings to enhance the movement of aquatic species as well as help road managers avoid tragedies, decrease much costlier emergency repairs and reduce expensive detours for travelers.
Explore examples of projects designed to address freshwater barriers that impact the movement of aquatic species, affect river health and impact people.
Protecting & Restoring Stream Flows
Obstacles aren’t an issue for aquatic species if there isn’t enough water to begin with. TNC employs an array of strategies aimed at improving or restoring “environmental” flows. Such work includes efforts to protect groundwater, modernizing the operations of dams, working with farmers to improve the efficiency of irrigated crops and the creation of water funds that help protect water sources and flows. See examples of such work.
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.
Select Freshwater Projects
Click on each square to learn more.
Addressing Dams & Culverts
- Helping shape Brazil’s hydropower future.
- TNC is helping remove obsolete dams and plan for new ones in Europe.
- The largest dam removal project in Connecticut.
- Dam removals are helping “free” Kentucky’s Green River.
- Two dam removals and a fish passage made a big difference at Maine’s Penobscot River.
- Dam removals in Massachusetts brought back to life a “once-dead” river.
- Removing old dams created new hope for New Hampshire’s Bellamy River.
- Removing a dam helped improve the health of the Delaware River.
- TNC has prioritized dam removals throughout Tennessee.
- Removing “deadbeat” dams is reconnecting and restoring Vermont’s “broken streams.”
- TNC scientists recently detailed efforts to streamline culvert improvements in Maine.
- TNC received NOAA grants to improve culverts and bridges in North Carolina to improve fish passage and river health.
- TNC helped the State of Georgia produce a handbook to help improve the design of roads that cross streams.
- Tidal gates can also be a barrier for migrating fish; learn how TNC in Oregon addresses these to benefit salmon.
- This article published in TNC’s magazine provides an overview of work to address barriers to fish migration and the other impacts they have on people and nature.
Freshwater Restoration
- The restoration of 3,000 floodplain acres along 14 miles of the once-“channelized” Pocomoke River in Maryland.
- Nearly 150 projects in Oregon benefit salmon.
- Several projects in Ohio, funded through the state’s mitigation program, are improving river health.
- Projects in Arkansas benefit the Cache and Kings rivers.
- The reconnection of a 3.5-mile-long side channel along the lower Mississippi River.
- Restoring meanders to Montana’s Ruby River.
- Big lessons learned from the restoration of Little Creek in Missouri.
- Protecting and restoring Chinook and steelhead habitat in the upper Snake River in Idaho.
- Restoring spawning habitat in the Great Lakes.
- Restoring wetlands on Hawaii’s island of O’ahu.
Restoring Wetlands & Floodplains
- A 25-square-mile floodplain reconnection at “Mollicy Farms” along the Ouachita River in Louisiana.
- A 6,700-acre project at TNC’s Emiquon Preserve along the Illinois River in Illinois.
- A series of habitat reconnection projects on the Willamette River in Oregon.
- A 1,040-acre levee “setback” project along the Missouri River in Missouri.
- Work in Washington’s Puget Sound benefits salmon.
- Giving more room to the Sacramento River in California.
- Restoring tidal wetlands benefits salmon in Oregon.
Protecting and Restoring Stream Flows
- TNC is behind a myriad of efforts to protect groundwater that also supplies much of the flows in our rivers and streams. Learn more.
- The Sustainable Rivers Program improves the way many large dams are operated to produce more benefits and minimize environmental impacts.
- We work with farmers to reduce the amount of water they use to irrigate their crops. Our work in Nebraska, Arizona, Arkansas and other several states serve as prime examples of this strategy.
- We’re working to address water flows and water scarcity in a variety of different ways throughout the drought-prone Colorado River Basin in the U.S.
- TNC and its partners manage 32 Water Funds initiatives around the globe that provide a steady source of funding for the conservation of more than 7 million acres of watersheds and secure drinking water for nearly 50 million people. Colorado’s Yampa River Fund employs a variety of strategies aimed at protecting flows, and water funds we’ve helped launch in Africa and India that focus on agriculture improvements do as well. In Ecuador, two water funds are aimed at protecting water—and flows—at headwater sources.
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
Dive Deeper
Sustainable Rivers Program
The Nature Conservancy and the U.S. Army Corps of Engineers are finding new ways to strike a sustainable balance in how people use and protect the many benefits that rivers provide.
The Comeback: Alewives Return To Maine Rivers
Many of Maine’s rivers are experiencing a remarkable comeback. One of the world’s great migrations is returning to our waters. We’re talking about alewives!
Unleashing Rivers
New England’s waterways—the most heavily dammed in the United States—are making a comeback.
