Dams on the lower Columbia River and several of its key tributaries have significantly harmed salmon and steelhead populations, and regulated flows have reduced the quantity and quality of habitat available to migrating salmon below Bonneville Dam. Further, Bonneville Dam is a significant barrier to adult chum salmon and inundated historic spawning habitat in the Columbia River and lower tributary reaches above the dam.
In tributaries, dams on the Cowlitz and Lewis Rivers eliminated access to areas that can support productive populations of Chinook and coho salmon and, steelhead. Hatchery programs were established to mitigate for the impact of these dams, but recovery will require restoration of access and reintroduction of these Endangered Species Act-listed populations to blocked habitats. Efforts to improve fish passage, collection and transport, hatchery management practices, and habitat quality and availability are ongoing.