Salmon and their cousins, steelhead, the ocean-going form of rainbow trout, are anadromous fish. The word comes from the Greek anadromous, meaning “to go, or run, uphill.”
That is what salmon and steelhead do. They hatch in freshwater, go to the ocean as juveniles, grow there to adulthood and return to the place of their birth, in some cases to streams that are hundreds of miles inland and thousands of feet above sea level, to spawn and die. Through anadromy, Pacific salmon and steelhead cause a massive exchange of nutrients from the ocean to rivers as far inland as the fish can travel.
Salmon and steelhead aren’t the only anadromous fish in the Columbia River Basin. Sturgeon and Pacific Lamprey also are anadromous. Lamprey are found primarily in the lower Columbia and Snake rivers. Sturgeon are found in the Columbia as far upstream as the international border. Sturgeon also have been caught in the lower Snake River. The sturgeon population in the U.S. Kootenai River and kokanee —landlocked sockeye salmon — in Kootenay Lake, British Columbia, are believed to have anadromous ancestors that became landlocked since the last Ice Age about 11,000 years ago.