New Report Evaluates Northeast Dams’ Ecological Impacts

Analysis Weighs Benefits of Dam Removal and Fish Passage Regionally

Concord, NH | 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 river herring and other fish begin their inland migration in a few weeks, 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 Conservation Freshwater 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 single best way to balance the human and natural resources our rivers provide is to know which dams provide benefits to both. That is, we know which dams benefit people by providing flood storage and hydropower,” said Douglas Bechtel, director of conservation science for The Nature Conservancy in New Hampshire. “With this report, we now also know which dams, if restored or removed, provide the most benefit for fish, wildlife, habitats, and all the natural resources rivers have provided for centuries. Many of those dams are in disrepair and are expensive to maintain,” he said. 

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 to resident fish species like brook trout; and can be used at the scale of states, regions or river basins.

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. 

Driven by both its numerous coastal streams as well as the Connecticut River basin, Massachusetts is behind only Maine and Virginia in the number of dams in with the highest potential impact on migratory fish. Of the 1,521 Massachusetts dams considered, 161 were in the top 10 percent regionally. 

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. 

But all dams are not created equal, 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. 

And in many cases, dam removal is a public safety issue. Throughout New England, dams that were constructed during the region’s early industrial years have fallen into disrepair and no longer serve an economic purpose, and many have become dangerous. In 2011, the Massachusetts state auditor identified 100 dams, owned by towns and cities, that are in poor condition or unsafe

In 2005, much of downtown Taunton, MA was evacuated, and homeowners suffered significant flood damage because just such a dam, on the Mill River, failed following a major rainstorm and flooding that led to emergency declarations in more than 40 communities. The combined benefits to public safety and the environment have prompted many Massachusetts lawmakers to support legislation, now pending on Beacon Hill, which would create a state loan program to fund dam inspections, repairs and removals. 

The Northeast Aquatic Connectivity Assessment report indicates the benefit of removing several dams on the Mill River in Southeast Massachusetts which are slated for removal in the coming years – placing them in the top 10 percent, Bowden said. In fact, the Whittenton Dam, which famously failed seven years ago, is scheduled to come out this summer. 

In the future, the assessment tool can help local leaders make this decision, before old dams become a public safety emergency, she said. 

“This ecological data is one piece of the puzzle for communities to use as they decide whether to remove or adapt dams,” Apse 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. Funding for the project was provided by State Wildlife Grant funding, awarded through the Northeast Regional Conservation Needs (RCN) Program, as 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. Visit The Nature Conservancy on the web at To learn about the Conservancy’s global initiatives, visit To keep up with current Conservancy news, follow @nature_press on Twitter.

Contact information

Misty Edgecomb
Senior Media Relations Manager
The Nature Conservancy

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