The sea lamprey, Petromyzon marinus, was first discovered in Lake Ontario in 1835, Lake Erie in 1921, Lake Huron 1932, Lake Michigan 1936, and Lake Superior 1946. Reproducing populations were found in all of these upper lakes by 1947. The sea lamprey attaches to deepwater fish, especially lake trout and chubs, for food and indirectly gains transportation that has enabled it to become widely dispersed throughout the Great Lakes. They remain attached and feed on the fish until they are satiated or until the fish dies. Lake trout, burbot and whitefish populations were devastated by lamprey predation by the early 1940s. Much work to control this parasite in the Great Lakes has been accomplished, but without continued control and research into stream invasions, the populations would once again escalate, damaging the predator/prey balance.