Invasive species are an ever growing problem in the U.S.  August 9, 2005, three voracious Snakehead Fish were discovered in Meadow Lake of Flushing Meadows-Corona Park, Queens New York. (Ref: New York Times 8/9/2005 page C15).

The snakehead is a top of food chain predator with rows of sharp teeth and a torpedo shaped body designed to ambush its prey.  They will literally wipe out all other fish in a lake or pond if allowed to reproduce unchecked.

-----there's also lots of squirrels.