A giant female Chinook salmon flips on her side in the shallow water and wriggles wildly, using her tail to carve out a nest in the riverbed as her body glistens in the sunlight. In another moment, males butt into each other as they jockey for a good position to fertilize eggs.

These are scenes local tribes have dreamed of seeing for decades as they fought to bring down four hydroelectric dams blocking passage for struggling salmon along more than 400 miles (644 kilometers) of the Klamath River and its tributaries along the Oregon-California border.