On the west coast, four large dams on the Klamath River, which flows from southern Oregon to northern California, are expected to be removed by 2022, rationalizing about 400 miles of habitat for migratory fish.
On the east coast, efforts are underway in Connecticut to eliminate obsolete river dams that connect with Long Island Sound.
State authorities are partly motivated by concerns about public safety, as aging dams can suddenly yield. "We have government regulations that say we will not allow you to let your dam collapse and kill people," said Stephen Gephard, a fisheries supervising biologist at the Connecticut Department of Energy and Environmental Protection. "Dangerous dams need to be inspected every two years."
Connecticut has about 4,000 dams, said Dr. Gephard, and the vast majority of them are obsolete. The state has about 100 dams and is reviewing the list to determine which should be removed. But Gephard's team identified 20 to 30 private dams that he would like to remove to allow fish to pass.
Gephard said it could take years to educate a community or a private owner about the merits of losing their dams, a process that often involves debunking myths. Some residents fear that they will have a stinking mud when the dam is gone, but in fact, dormant seeds quickly become trees, shrubs and grasses.
"The most bizarre myth is the notion that if you remove the dam, there will be no water in the stream," said Gephard. "It's like they think the water comes from this concrete. Many Americans don't understand the concept of a watershed or running water."
To that end, conservation groups have recruited engineering companies to create photographic representations showing how a river would appear without a dam, said Dr. Gephard.