It’s been less than a year since the world’s largest dam removal project was completed along 420 miles of the Klamath River, near the border of Oregon and California. But if you look at the river now, you might not know that four dams had ever been in place. Instead of concrete walls and artificial reservoirs, the river is now free-flowing—and parts of the former infrastructure have been replaced by wildflowers that are in bloom.

“It’s been an incredible transition,” says Ann Willis, California regional director at American Rivers, a nonprofit that supported Native American tribes in a decades-long fight to take out the dams. “It’s really strange and wonderful to stand on the bridge that goes across the Klamath River and look upstream where Iron Gate Dam used to be. I used to imagine a river above it, and now I see the river.”

The dams were built between 1918 and 1962 to provide hydropower, and immediately blocked salmon from migrating. Over time, the ecosystem started to collapse. By 1997, coho salmon in the river were listed as endangered. (The river was once the third-largest salmon fishery in the continental U.S.) In 2002, when the federal government diverted water to........

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