Biologists say Great Lakes still at risk despite ballast flushing

The Canadian and U.S. operators of the St. Lawrence Seaway have begun requiring freighters to flush their ship-steadying ballast tanks with ocean saltwater to kill or expel any unwanted organisms before they arrive in the Great Lakes.

Seaway advocates say the flushing largely has solved the ballast problem, and point to the fact that no new species have been detected in the lakes since late 2006.