The latest threat to Great Lakes fisheries could be Asian carp, which are heading north in the Mississippi River system toward Lake Michigan.

Asian carp were imported in the 1970s to control algae in commercial fish farms, but they escaped into the Mississippi watershed and began multiplying rapidly. These large carp eat vast amounts of zooplankton and have no natural predators once they reach their adult size of 50 to 100 pounds.

The only thing preventing the carp from entering Lake Michigan is an electric shock barrier placed in a Mississippi River Canal in Illinois. However, the barrier costs $700,000 per year to operate, and funding for the project will run out in October 2003.