Why are salmon in trouble? - Dams

Dams are probably the most publicized problem for salmon. Dams can block or impede migration and have created deep pools of water that in some cases have inundated important spawning habitat or blocked access to it. Dams also change the character of rivers, creating slow-moving, warm water pools that are ideal for predators of salmon. Low water velocities in large reservoirs also can delay salmon migration and expose fish to high water temperatures and disease.

Many things have been done to reduce the impacts of dams on fish. Fish passage facilities and fish ladders have been developed to help juvenile and adult fish migrate around many dams. Spilling water at dams over the spillway is an effective means of safely passing juvenile fish downstream because it avoids sending the fish through turbines. Water releases from upstream storage reservoirs have been used to increase water velocities and to reduce water temperatures in order to improve migration conditions through reservoirs. Juvenile fish also are collected and transported downstream in barges and trucks.

Many other solutions to the problems that dams pose have been suggested – including removing them. A number of small dams in the Pacific Northwest that block salmon migration have been removed or are being considered for removal. The removal of larger hydroelectric dams, such as those on the lower Snake River, has been very controversial and currently is not being considered as an option.

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