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New Report Evaluates Northeast Dams’ Ecological Impacts

Analysis Weighs Benefits of Dam Removal and Fish Passage Regionally

NEW HAVEN, CT | 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.

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. About 1,700 of the estimated 5,000 dams in Connecticut were assessed.

“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, deputy director of The Nature Conservancy’s North America Freshwater Conservation Program 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 over three years; using GIS technology to calculate more than 70 different metrics that affect habitat in the Northeast’s extensive river systems.

The database that they produced 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. An assessment tool can be customized to consider either anadromous fish like Atlantic salmon, shad and alewife that migrate between fresh and saltwater environments, or resident fish species like brook trout; and can be used at the scale of states, regions or individual river basins.

“River herring, a harbinger of spring, are returning to Connecticut’s rivers now,” said Sally Harold, The Conservancy’s Connecticut director of migratory fish projects. “These fish need to reach freshwater habitats to successfully spawn; yet along Connecticut’s 100-mile coastline there are few rivers without dams—and only so far these fish can go. This project will help guide us to potential projects at dams that will provide the greatest environmental benefits.”

Maine and Virginia have the most dams in the top 10 percent regionally for potential benefits for migratory species, although Massachusetts, New Jersey and Delaware also have significant results 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.

Across the assessment region, 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 in important role in providing energy, flood control, or recreational opportunity. Some create drinking water supplies, 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 well as The Nature Conservancy’s Connecticut River Basin Program.

The full report is available online 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 on the web at

The Nature Conservancy is a leading conservation organization working around the world to conserve the lands and waters on which all life depends. The Conservancy and its more than 1 million members have protected nearly 120 million acres worldwide. Visit The Nature Conservancy on the Web at

Contact information

James Miller
Media Relations Manager
The Nature Conservancy

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