Experts say fishways meant to give fish a route around dams have failed to let economically important species such as salmon, shad and river herring reach their spawning grounds.
Despite state-of-the-art fish passage facilities, the numbers of fish passing through them over several decades reached only a tiny fraction of targeted goals, they said.
"It may be time to admit failure of fish passage and hatchery-based restoration programs and acknowledge that ecologically and economically significant diadromous species restoration is not possible without dam removals," the researchers wrote in the journal Conservation Letters.
Diadromous species are fish that migrate from the sea to spawn in rivers.
The three river systems studied, the Merrimack, Connecticut and Susquehanna, are historically important to populations of such species, researchers said.
Numbers of American shad, once one of the country's premier food fish, hovered around 2 percent of the target in the Merrimack River and was close to zero percent of target in the other two, they said.
"These dams are contributing to reduced resilience of not only shad, but all diadromous species," said Adrian Jordaan of the University of Massachusetts Amherst.
The findings raise serious questions about the impact of new dams now being planned and constructed on major waterways worldwide, the researchers said.
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