The destructive effect on the Great Lakes fishing industry caused by the invasion of the sea lamprey is well known. The opening of the Welland Canal in 1829 first gave the species access to the upper Great Lakes, and it now occurs through the entire system.

Originally, sea lampreys were found only in the Atlantic Ocean, near eastern North America, Europe and northern Africa. The Great Lakes hold the only landlocked populations.

In general, sea lampreys reach a maximum size of about 76 cm (30 in.), although most individuals are somewhat smaller.

The adults live as external parasites of a variety of fish, in fresh water. They attach themselves to the body of the host by means of the sucking disc, which is ringed with sharp teeth, and rasp a hole through the victim's skin. The sea lamprey's food—the fish's blood and body fluids—are thus consumed. The attachment can last from 38 to 220 hours.

Long considered a delicacy by European diners, the sea lamprey has, so far, failed to whet North American appetites.