When ships take on cargo they also may pump water into ballast tanks to balance the load. When they off-load they sometimes pump out their ballast tanks. That water, from foreign ports, may release fish and other aquatic species not found in the Great Lakes.
Up to now, foreign vessels just had to exchange their ballast water before they entered the lakes, and the U.S. Coast Guard has really clamped down in recent years, making sure that happens, according to Spokesman Lorne Thomas.
The Coast Guard has studied this issue for more than decade.
Michigan regulators aren't convinced that's the best approach. They say a tougher standard would push development of better technology.