Here Kirk Cowen (right) and Eric Harms (left) of the Illinois River Biological Survey attempt to net some crazed leapers.

The invaders -- primarily silver and big-head carp -- are plankton eaters, chowing down on the same tiny invertebrates that gizzard shad and other small fry dine upon. Too many carp in the water and they'll suck out the bottom of the food chain. This creates a domino effect that imperils game fish like walleye and bass.

"If the Asian carp gets into the Great Lakes we're in serious trouble," says Dennis Schornack, U.S. chair of the Great Lakes International Commission. "We could see a $4.5 billion fishing industry go down the tubes."