Adult Migration Over Dams & Through Reservoirs

When salmon and steelhead return to the Columbia River as adults, they have similar physiological needs (stressors) to make the transition to the freshwater environment. They do not eat during the journey to their spawning grounds, so they depend on large fat and protein reserves for swimming upstream and egg/sperm development for spawning. Precious energy is expended as the fish cross the dams via steep fish ladders. Warming reservoirs add stress to their passage.

An estimated 25% of adult spring/summer chinook and 35% of adult steelhead die as they migrate upstream through the 8 dams via fish ladders. Additional mortality occurs after the fish have passed the last dam headed toward the spawning grounds. An intensive survey in the South Fork of the Salmon River revealed from 15 to 60% of adult summer chinook can die before spawning. Causes include extended migrations, stress from elevated water temperatures, energetic exhaustion, disease and delayed mortality due to falling back over the dams.

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