May 14, 2008 — Cargo ships move sea life around the world. Many of the more then 185 invasives in the Great Lake and St. Lawrence River hitchhiked in the ballast water of the freighters. From zebras mussels to the round goby, they can cause environmental havoc. Earlier this week, David Sommerstein reported on a new technique for treating ballast water before it reaches the St. Lawrence. Called "swish and spit," it requires ships to rinse their ballast tanks with seawater offshore. The seawater kills most organisms that would live in the fresh water of the river and the lakes. But there's another idea in the works -- Lester Graham has more on why ballast water is so important, and how a new ship design could nearly eliminate the problem altogether.