KRT Wire has this interesting report about rusty crayfish (Orconectes rusticus) invading Wisconsin waters. Introduced as bait several decades ago, the crayfish often cause problems in lakes by detroying aquatic vegetation, upsetting the balance of the ecosystem and reducing fish populations. Brian Roth, a grad student at the University of Wisconsin, Madison, has been studying the crayfish and thinks he has found a good management solution: add more bluegills (Lepomis macrochirus) and give the predatory fish the advantage. He will be testing his hypothesis this summer.
(Okay, okay, the article calls them "rusty crawfish", but I live in the land of the "scawllup" and we call 'em crayfish).