Migration rates of yearling Chinook salmon (Oncorhynchus tshawytscha) through freeflowingand impounded stretches of the Snake and Columbia Rivers were compared duringperiods of low and moderate river discharge. Generally, the rate of migration was directly relatedto the water flows; it was 21 km/day at the low river discharge (Columbia - 4,248 m3/sec; Snake -1,416 m3/sec), and 37 km/day during moderate river discharge (Columbia - 8,495 m3/sec; Snake -2,265 m3/sec). Migration rates through most free-flowing and impounded stretches of the Snakeand Columbia Rivers were similar with the one exception that in McNary Reservoir (ColumbiaRiver) fish moved only about one-third as fast as elsewhere.Marked yearling Chinook salmon from the Salmon River took 32 days to travel the 669 km toBonneville Dam during the low river discharge in 1966. New impoundments may more thandouble the travel time now required during low river flows.