Most salmon migrate from the sea into fresh water to spawn. This became difficult during the last Ice Age, when populations of salmon were cut off from icebound spawning grounds. A study recently published in Quaternary Research, led by fisherman-scientist Patrick Martin, used genetic analyses of more than 32,000 chum salmon to suggest that some populations survived the last Ice Age isolated in freshwater glacial lakes. The researchers propose that salmon trapped in these lakes treated them like miniature oceans, migrating up glacial streams to spawn. This prolonged isolation could explain the unusually high genetic divergence and distinctive life-history traits observed in some populations in Alaska and the Salish Sea. UW researchers David Montgomery, Harvey Greenberg, and Ralph Haugerud are co-authors.