Dams restrict fish passage to the ocean and back to spawning grounds. There are two major issues with dams. Dams block fish passage upstream to areas where salmon once reproduced and spent their early lives. Grand Coulee on the Columbia River and Hells Canyon on the Snake permanently block 1,200 miles of those mainstem rivers once used by salmon. Similarly, dams block rivers and streams in the Willamette Valley, central Oregon, Klamath County and southeastern Oregon.
Dams reduce the number of juvenile salmon that migrate downstream to the ocean.
On the Columbia-Snake system, juvenile salmon that remain in the river on their downstream migration must pass eight dams. The dams also create a series of lakes, slowing the current and delaying downstream migration. The delay interferes with internal biological changes that enable the young salmon to survive in saltwater. In addition, the slack water exposes them to northern pikeminnows, also known as squawfish, and other predators, including several introduced species, walleye and bass. Install screens and bypass systems to divert fish away from turbines.