Tickleback evolution lab final quiz 1. how did some ancestral sea-run stickleback populations come to live exclusively in fresh water? these populations swam to freshwater lakes to spawn and then never returned to the ocean because there were fewer predators in lakes. they became trapped in lakes that formed at the end of the last ice age. they don't actually live exclusively in fresh water; they only live in fresh water at certain stages in their lives. they developed traits that made them better adapted to fresh water and, as a result, had to move to a freshwater environment to survive.