New Report Evaluates Northeast Dams’ Ecological Impacts

Analysis Weighs Dam Removal Regionally; Penobscot Dams Receive High Score for Potential Benefits of Dam Removal

BRUNSWICK, ME | March 26, 2012

The Northeast has the dubious honor of some of the nation’s most fragmented river systems, with an average of seven dams interrupting every 100 miles of river. When alewife and other fish begin their inland migration from The Gulf of Maine later this spring, they’ll face a gantlet of dams.

Now, a team of biologists and policy experts from throughout the region has developed a means of weighing the ecological impact of these dams, data that can be critical to securing and targeting limited funds for river restoration efforts. Their report, titled Northeast Aquatic Connectivity: An Assessment of Dams on Northeast Rivers, was released to the public today.

“For the first time, we can easily quantify and compare how removing different dams might affect the ecology of river systems throughout the Northeast, allowing us to more successfully work at the scale of nature,” said Colin Apse, Senior Freshwater Conservation Adviser at The Nature Conservancy, and a lead scientist on the project.

Staff members from state and federal wildlife agencies, local universities, The Nature Conservancy and other conservation groups collaborated, over several years, to analyze myriad data sources; using GIS technology to calculate more than 70 different metrics that affect habitat in the Northeast’s vast interconnected river systems.

The database considers nearly 14,000 dams in thirteen states and the District of Columbia, and identifies locations where dam removal or fish passage construction would likely have the most significant ecological benefit. The assessment tool can be customized to consider either anadromous fish − like the Atlantic salmon, sea lamprey, Atlantic sturgeon, American eel and alewife that migrate between the sea and Maine’s freshwater lakes and streams − or to resident fish species like brook trout. The tool can be used at the scale of states, regions or even river basins.

 Maine has the most dams in the top 10 percent regionally for potential benefits for migratory species, although Virginia, Massachusetts, New Jersey and Delaware also have significant results, particularly when river length is considered. All the states in the analysis − from Maine to West Virginia − have one or more dams that rank high for the potential benefits of fish passage restoration, as do each of the major river basins in the region.

And several of the major dams that are part of the Penobscot River Restoration Project appear in the top 10 percent regionally for their potential to improve fish passage. The project includes removal of the Great Works Dam, as well as the removal of the Veazie Dam and installation of a fish bypass at the Howland Dam – all of which score high on the connectivity analysis. The Penobscot River Restoration Trust purchased the three dams in 2010, and will begin work this summer.

And Black Bear Hydro, LLC, which operates several other hydroelectric dams in the region, plans to install a new fish lift and eel ladder at its Milford Dam, which also places in the top 10 percent. Taken together, these and other efforts to improve fish passage within the Penobscot River basin can balance energy production with other ecological and community needs – precisely the sort of effort that The Nature Conservancy believes is necessary to restore New England’s rivers.

“This project will restore access to habitat for a dozen species of sea-run fish, by opening over 1,000 miles of river that has been inaccessible for nearly two centuries. It’s exciting to see the data reaffirm what we’ve long said about the likely benefits of the Penobscot River Restoration,” said Mike Tetreault, Executive Director of The Nature Conservancy in Maine, which is one of the members of the Trust.

Across the Northeast, dozens of dams have been removed in recent decades, restoring natural habitat to many rivers. But as funding for conservation faces ever more substantial budget cuts at all levels of government, scientists must demonstrate the return on these public investments in ecological restoration.

“The Northeast Aquatic Connectivity project is a useful tool and first step in deciding how best to allocate state resources on the projects most likely to improve fish habitat,” said Glenn Normandeau of New Hampshire Fish and Game, and President of the New England Association of Fish and Wildlife Agencies, a key partner on this project.

And not all dams need be removed. In some cases, dams play an important role in providing energy, drinking water or recreational opportunity, or dam removal simply isn’t feasible. Community and conservation leaders can use this tool to consider the ecological benefits of dam removal or fish passage installation. Combined with on-the-ground data about economic and community needs, it will provide a more complete picture to inform local decisions, Apse said.

“This ecological data is one piece of the puzzle for communities to use as they decide whether to remove or adapt dams,” he said. “It isn’t about removing every dam. It’s about removing the right dams, and using limited funds for the greatest benefit.”

States assessed in the Northeast Aquatic Connectivity Assessment include; Maine, Vermont, New Hampshire, Massachusetts, Connecticut, Rhode Island, New York, Pennsylvania, New Jersey, Maryland, Delaware, West Virginia and Virginia, as well as the District of Columbia.

This project was supported by State Wildlife Grant funding awarded through the Northeast Regional Conservation Needs (RCN) Program. The RCN Program joins 13 northeast states, the District of Columbia, and the U.S. Fish and Wildlife Service in a partnership to address landscape-scale, regional wildlife conservation issues. Progress on these regional issues is achieved through combining resources, leveraging funds, and prioritizing conservation actions identified in the State Wildlife Action Plans. See for more information. Funding was also provided by The Nature Conservancy’s Connecticut River Basin Program.

The full report is available online at:

More information about the Penobscot River Restoration Project is available at



The Northeast Association of Fish and Wildlife Agencies represents the region’s fish and wildlife agencies to advance sound, science-based management and conservation of fish and wildlife and their habitats in the public interest. Visit NAFWA online at


The Nature Conservancy is a leading conservation organization working around the world to protect ecologically important lands and waters for nature and people. The Conservancy and its more than 1 million members have protected nearly 120 million acres worldwide. Visit The Nature Conservancy on the Web at

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Misty Edgecomb
Senior Media Relations Manager
The Nature Conservancy

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