Native to Pacific Slope from Kuskokwim River, Alaska to (at least) Rio Santa Domingo, Baja California, Mexico; upper Mackenzie River drainage (Arctic basin), Alberta and British Columbia in Canada; endorheic basins of southern Oregon, USA. Widely introduced in cold waters elsewhere in North America and rest of the world (Ref. 5723). Eastern Pacific: Kamchatkan Peninsula and have been recorded from the Commander Islands east of Kamchatka and sporadically in the Sea of Okhotsk as far south as the mouth of the Amur River along the mainland. The records outside Kamchatka probably represent migrating or straying Kamchatkan steelhead (penshinensis) rather than the established native population (Reg. 50080). Several countries report adverse ecological impact after introduction.