Sea lamprey invasion (1930s-1950s)
Sea lamprey, a parasitic, eel-like fish, reached the upper Great Lakes through the Welland Canal. By the 1950s they had devastated lake trout and other large predators, collapsing commercial harvests across Lakes Huron and Michigan.
The Great Lakes Fishery Commission began a permanent chemical and barrier control program that still runs today.
The lamprey was never eliminated, only controlled, setting the precedent that an established invasive species cannot be removed.
The carp threat is the same: once established in Lake Michigan, experts say the fish are there permanently.
