Biologists fear that the ruffe's spread towards the lower Great Lakes may reduce populations of valuable sport and commercial fish. It is now commonly seen on fishing lines in Lake Superior during late summer. B.C., which can grow to about one-half inch long, might compete with small fish for food by eating smaller zooplankton. Unfortunately, larval fish that feed on zooplankton cannot eat B.C. because it is fairly large and has a long, spiny tail. Although the zebra mussel is causing severe problems in the other Great Lakes, it is only occasionally found in Lake Superior and the Duluth-Superior harbor, and does not appear to be reproducing.
Large numbers can attach to and clog the interior surfaces of boat motors and water intake pipes.
Zebra mussels can also attach to native mussels and smother them. It was found in the Duluth-Superior harbor in 1995 after first appearing in the Great Lakes in the St. Clair River in 1990. Once introduced into new waters, the population of this bottom-dwelling fish increases rapidly. The round goby, ruffe, B.C., and the zebra mussel are thought to have entered the Great Lakes in ballast water discharged from oceangoing vessels. Requirements that ships exchange ballast water in mid-ocean may reduce the likelihood of other exotics entering and disrupting the Great Lakes ecosystem.