Juvenile Chinook salmonOncorhynchus tshawytschawere collected from May to June 1980 in seven nonnatal tributaries of the lower Fraser River in British Columbia, Canada. The juveniles were collected predominantly in pools and had migrated 0.4–6.5 km up the nonnatal tributaries to reach the rearing areas. In 1981, two of the tributaries, Nathan Creek and the Brunette River, were sampled every 2 weeks from late February to late June. During this period, the mean fork lengths of juvenile Chinook salmon increased from 45 to 80 mm in Nathan Creek and from 44 to 68 mm in the Brunette River. The use of nonnatal rearing areas is of importance to the survival and productivity of juvenile Chinook salmon in the Fraser River.