Dec 08, 2009 — For decades now, invasive species have been one of the biggest threats to the health and economy of the St. Lawrence River and Great Lakes regions. More than 180 invaders have snuck into the watershed, most hidden in the ballast tanks of foreign Seaway ships. Things like zebra and quagga mussels, the round goby, and the sea lamprey crowd out native species, disturb the ecosystem, and have cost the region billions of dollars. But scientists and shippers are cautiously optimistic they're on the right track to keeping new invaders out of the St. Lawrence and Great Lakes. David Sommerstein reports.