Ships Release New Species into the Great Lakes

Analysis of ballast water recently carried by ships into the Great Lakes indicates that more exotic species will likely invade the freshwater ecosystem. At least 17 non-native species were stowed away in ballast water and entered the Great Lakes between 2000 and 2002. Thirteen of these species had not previously been living in the Lakes.

Most of the new organisms are small crustaceans such as copepods. Despite arriving in sea water, many of the introduced species can also survive in fresh water.

Since the St. Lawrence Seaway opened the Great Lakes to ocean-going vessels in 1959, ballast water has been implicated in establishing 46 new species there. Ships arriving from other ports are required to exchange their ballast tanks in mid-ocean to prevent them from transporting new species into the Lakes. But the results of this study indicate that even this precaution is not enough to stop arrivals of exotic species.