Salmon-killing McNary Dam was erected on tribal fishing sites in the Columbia River. Most of the hydro-power from the dam went to now-defunct aluminum mills and the Hanford Nuclear Reservation. Photo: Jeffrey St. Clair.

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. Europeans began erecting river barriers soon after they arrived in North America. Massachusetts’s Old Oaken Bucket Pond Dam, built in 1640, is one of the country’s oldest known dams. Thousands more followed across New England, then down the East Coast, and eventually westward. They powered mills that ground corn, cut lumber, forged tack, and produced textiles. As dams raised the height of the water behind them, they also smothered rapids and white water so that logs could be floated from upstream forests—where they were felled—to downstream industry, where they were processed. After hydroelectric power replaced mechanical power in the 1880s, the dams kept towns and cities alight.

As dam building pushed westward, dam heights pushed skyward. Hoover Dam, built in the 1930s with the labor of 21,000 men, sits 726 feet high and more than 1,200 feet long—more a fortress than infrastructure. Grand Coulee Dam on the Columbia River in Washington rises to 550 feet and stretches nearly a mile long. 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.

The U.S. Bureau of Reclamation, which built many of the country’s mammoth dams and reengineered its rivers, had a motto: “Our rivers: total use for greater wealth.” Millions of Americans cashed in on the boom, often without giving it a thought. Politicians and regulators championed dams for their power, flood control, water storage, and recreational potential. Indeed, dams shaped the architecture of the West, irrigating millions of arid acres to grow crops for people and livestock, corralling drinking water for cities hundreds of miles away, churning the engines of war to create aluminum for fighter........

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