Travel time for yearling chinook salmon (Oncorhynchus tshawytscha) to migrate the 370 km downstream from the Salmon River to Ice Harbor Dam was compared during 3 years prior (1966–68) and 4 years after (1970–74) impounding of the Snake River behind Lower Monumental and Little Goose dams. Prior to impounding, fish averaged 15 days of travel time to Ice Harbor Dam during low flows (1,000–2,000 m3/s) and 9 days during moderate flows (2,300–4,000 m3/s). After the new impoundments, average travel time was increased to 31 days in low flows and 20 days in moderate flows–a measured delay of 16 and 11 days, respectively.