Dams impact steelhead in a number of ways. Dams block passage of salmon and steelhead as migrating juveniles on their way to the ocean as well as on their return to freshwater rivers to spawn (often hundreds of miles upstream). Some dams include fish passage via fish ladders, although the effectiveness of these structures can vary widely. Capturing, trucking, and then releasing steelhead around dams has been done for years with variable success. Where fish passage structures or a truck ride is not provided, the blockage is permanent.
Dams alter habitat by inundating spawning areas, rearing habitat, and historic river flow patterns. This alternation to the river dynamics affects the entire ecosystem upstream and downstream. Unnatural fluctuating flows caused by power demands on hydro-electric dams have had lasting effects on steelhead populations. Spawning redds and newly hatched juvenile steelhead have been stranded as water floods and then quickly recedes from critical habitat. . Dams can also result in raised water temperatures, greatly affecting the aquatic ecosystem. Unnaturally increased water temperatures decrease dissolved oxygen levels, alters the food web including steelhead forage, and may decrease steelhead spawning success. As a dam slows the flow of water, it also cripples a river’s critical ability to keep in balance and transport sediment through the system. This can lead to siltation, the smothering of steelhead spawning areas, and buildup of toxic elements in the substrate.
A great example of how detrimental dams can be is readily seen in the Columbia River Basin of Oregon and Washington. More than 55 % of the spawning and rearing habitat once available to salmon and steelhead in the Columbia River Basin is permanently blocked by dams, and it is estimated that 70-95% of the human-induced mortality of salmon and steelhead in the Columbia River Basin is dam related.