The population structure of ‘lake-type’ and ‘river-type’ sockeye salmon Oncorhynchus nerka, primarily in transboundary rivers in northern British Columbia, was examined with a survey of microsatellite variation. Variation at 14 microsatellite loci was surveyed from c. 3000 lake-type and 3200 river-type sockeye salmon from 47 populations in six river drainages in British Columbia. The mean FST for the 14 microsatellite loci and 47 populations was 0·068, and 0·034 over all river-type populations. River-type sockeye salmon were more genetically diverse than lake-type sockeye salmon, with expected heterozygosity of river-type sockeye salmon 0·72 and with an average 12·7 alleles observed per locus, whereas expected heterozygosity of lake-type sockeye salmon was 0·65 with and average 10·5 alleles observed per locus. River drainage of origin was a significant unit of population structure. There was clear evidence of genetic differentiation among river-type populations of sockeye salmon from different drainages over a broad geographic range in British Columbia.