There has never been a confirmed sighting of a bull shark in the Great Lakes. Definitely up the Mississippi as far as Iowa, and once in the Ohio River a dead one was found but pretty safe to say they get in the Ohio all the time.

The Great Lakes are just not a comfortable temp for BULL* sharks and while one could survive during the warms months I don't think environment suits them from a hunting aspect, they aren't deep water predators.

Edit: *forgot to specify bull sharks