After centuries of dam building, a nationwide movement to dismantle these aging barriers is showing how free-flowing rivers can restore ecosystems, improve safety, and reconnect people with nature.

With more than 550,000 dams in the United States, free-flowing rivers are an endangered species. We’ve dammed, diked, and diverted almost every major river in the country, straightening curves, pinching off floodplains, and blocking passage for fish and other aquatic animals. But this has come at a great cost. Freshwater biodiversity—all the organisms that hail from our rivers, streams, lakes, and wetlands—is among the most threatened on the planet. Dams have played a big role in that demise, pushing fish, mussels, and other animals to the brink, and some over it. In North America, nearly 40 percent of fish are imperiled, and 61 species have blinked out since 1900.

A growing dam removal movement has led to some 2,200 dams being blasted and backhoed from U.S. rivers—most of them in the past 25 years. It’s an extraordinary turn of events for a dam-loving country. //

The United States emerged from the Great Depression into a dam-building frenzy that lasted more than 30 years, dubbed the “go-go years” by Marc Reisner in Cadillac Desert, his iconic book on western water. Between 1950 and 1979, approximately 1,700 dams were built each year.