Once in their new homes, the uninvited immigrants can multiply quickly and wage war on native species, gobbling up their food and stealing their habitat. Among the most notorious are the parasitic sea lamprey, which decimated the native trout population by the mid-1900s, and the zebra mussel, which arrived in the late 1980s and did hundreds of millions in damage by clogging water pipes. Governments around the world are trying to close their borders to unwanted biological travelers. But the sense of urgency is particularly strong in the Great Lakes, where nuisance aliens have drastically altered the world's largest surface fresh water system. More are on the way, scientists warn.
Shipping companies say they have made good-faith efforts to flush out the pests.
And the Coast Guard requires ocean freighters to dump their ballast and take on more water before entering the lakes via the St. Lawrence Seaway. Critics say more is needed. Sterilization a Problem Bills proposed in the Michigan, Minnesota and New York legislatures would order shippers to sterilize ballast, using government-approved methods of killing every critter, before dumping it into waters under their jurisdiction. A similar bill is pending in the U.S. House, and the Ontario provincial legislature also is considering ballast legislation. Possible ballast sterilization methods include heating water, chemical disinfectants, ultraviolet light, screens and filters.