In some waters, it's been reported that around 90 percent of the fish are invasive carp; in one section of the Illinois River, a Mississippi tributary, they make up more than 75 percent of the total biomass in the water. They are obnoxious invaders, overwhelming other fish species, muddying clear waters, and — in some cases — jumping out of the water when startled. A passing boat can throw hundreds of fish into a frenzy, creating an airborne blizzard of 25-pound lunkers that have broken the arms and jaws of recreational boaters.