Asian carp are infiltrating major American waterways; with insatiable appetites they have the power to destroy an entire ecosystem by depleting a native food chain from the bottom up. NGC takes to the waters to understand these alien predators. How did they get here? Where are they going? And what are scientists and anglers doing to fight back? We'll also look at some of the controversial methods being used to combat the fish, including underwater electric fences and bow-fishing.