The northern migration of Asian carp moves like the slow drip of a lethal IV. A grass carp, one of four Asian carp species loose in American waters, was recently caught in the Lower St. Croix River near Prescott, Wisc. Though grass carp have been caught in the Mississippi River between Minnesota and Wisconsin, this fish was found in waters previously thought to be carp-free. This particular species consumes up to 40 percent of its weight in aquatic vegetation per day. Such an appetite could destroy the habitat for native fish.