Oct 24, 2005 — This week we begin an extensive series on ten threats to the Great Lakes, with a look at some of the earliest invasive species. There are more than 160 non-native species in the Great Lakes basin. If they do environmental or economic harm, they're called invasive species. There are estimates that invasive species cost the region billions of dollars a year. David Sommerstein tells us how some of the region's earliest invaders got into the lakes.