A fisherman wades in the Kennebec River.
FREE-FLOWING Removal of the Edwards Dam on the Kennebec River has drastically improved habitat for migratory fish species—and fishing opportunities—along the river and its tributaries. © Bridget Besaw

Climate Change Stories

Removing Barriers to River Health

While many large dams in North America deliver invaluable services—like critical water supplies, clean hydroelectric power, reduced flood risks and recreational opportunities—many more no longer serve their intended purpose and create serious safety and environmental concerns. Globally and in the United States, dams and levees are among the greatest threats to river and wetland health and resilience. 

The Comeback Watch a short animated video that helps explain the value of free-flowing rivers.
Underwater photo of a dense school of herring.
RIVER HERRING Unimpeded by dams or poorly designed culverts, these herring swim upstream to spawn in the Spring. © Eric Aldrich / TNC

20 Years of Restoring Healthy Rivers through Dam Removals

On July 1, 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. 

Twenty years later, The Nature Conservancy celebrates the efforts of the Natural Resources Council of Maine, American Rivers, the Atlantic Salmon Federation, Trout Unlimited and other partners that made this success a reality. 

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.

Since 1999, the restoration of fisheries on the Kennebec has continued. In 2008, a dam was removed from the Sebasticook River, an upstream tributary, adding many more miles of free-flowing river for migratory species. Together with fish passage added at several upstream dams, the removal of the Edwards Dam started the restoration of access to 130 river miles and 9,800 acres of ponds—all essential for sea-run fish migration and spawning.

In 2018 over 5 million migratory alewives—a type of herring that are critical food sources for larger species—returned to the Sebasticook River, making it the largest alewife run in the United States. With the renewed fishery and water quality improvements, the communities around the Kennebec have also seen improved boating and fishing opportunities.

With this dam removal, partners started a movement for free-flowing rivers, sustainable fisheries and healthier communities. The project also served as an inspiration for inter-agency collaboration with non-profit organizations and paved the way for similar efforts, including Maine’s Penobscot River, where more than 2,000 river miles have been restored. 

Since 1999, 1,199 dams have been removed in the United States, resulting in the restoration and improved health of tens-of-thousands of miles of free-flowing rivers. 

A participant in the "Katahdin 100", an annual Penobscot Tribe journey, beats a drum greeting to canoes on the Penobscot.
PENOBSCOT RIVER The Conservancy played a pivotal role in removing two dams on Maine’s Penobscot River and building a fish bypass around a third, giving 12 native species of sea-run fish access to thousands of miles of habitat along the river system, much of which flows through Native American tribal lands. © Bridget Besaw

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
Dam Removal in Randolph, Vermont The Conservancy’s recent role in the removal of an obsolete dam in Vermont reconnected more than 100 river miles for migratory fish and created additional benefits.

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 a related article 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.
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