Look for news articles on the Asian Carp in the illinois river. They are a hazard to boaters because they get irritated by the noise of a motor and jump out of the water. Nothing like a 20 pound carp smaking you in the side of the head while your baoting. Back to the ecosystem, there is a great fear that these carp will get into the great lakes and rapidly rewrite the food chain, and general environment of the great lakes. Also check out the zebra mussels, in Lake erie and many ohio lakes, they IMO have done more good than harm but still are uncontrollable, and change the ecosystem of every body of water they are introduced to.