Lampreys are an ancient group of fishes that do not have jaws. Because of their jawless, disc-like mouth, they can cling to almost any wet surface and can climb waterfalls. However, they cannot move around sharp corners in high flows and have trouble passing fish ladders made for salmon.
Pacific lampreys in Idaho may be found in tributaries to the Snake, Clearwater and Salmon rivers.
Adult Pacific lampreys leave the ocean during June and July to migrate upstream. Like salmon and steelhead, they do not feed after they leave the ocean. They spend the winter in the river before spawning late May to early July and die soon after.
Young lampreys are eyeless and burrow into sand where the current is slow. There they live for 3 to 7 years feeding on algae and bits of plant or animal material. When they are large enough, they grow eyes and move downstream to the ocean during the spring. In the ocean they live as parasites on other fishes for 1 to 3 years. Little is known of their ocean movements.