Aug 08, 2008 — The ballast tanks of foreign Seaway ships are the number one vector of invasive species in the St. Lawrence River and Great Lakes. Invaders like the zebra mussel and round goby cost the region hundreds of million dollars a year. Some environmentalists and scientists have called for the Seaway to turn away foreign freighters until they install sophisticated treatment systems to clean the ballast tanks. A new report by the National Academy of Sciences says that's not necessary. The 4-year study by 13 scientists says rules adopted this year requiring all foreign ships to flush their ballast tanks with salt water before entering the Great Lakes are sufficient. U.S. Seaway Adminstrator Terry Johnson praised the committee's findings. He said closing the Seaway to foreign traffic would be "legally unfeasible, politically unrealistic, and economically disastrous" for the U.S. and Canada. Hugh MacIsaac was a member of the study team. He researches invasive species at the University of Windsor in Ontario. MacIsaac told David Sommerstein that salt-water flushing of ballast tanks, known as "swish and spit," is the best existing way to stop invasives. And it lacks the political controversy closing the Seaway to foreign ships would have.