We now have a SERIOUS problem with Zebra Musscles in the great lakes.More specifically Lake Michigan.Although they were introduced by accident,ships dumping thier ballast/bilg water into the lake,They are now growing out of control...They are even litterally clogging the intake screens of out water treatment,and power plants...The upside of this is that they are filter feeders,and the lake is noticalby clearere than it has ever been.Although it seems as I am about the only one that sees this as a plus....