Bull shark.
:^)
Bingo!
I’d have to see a lot more evidence before I could conclude that it was a Bull Shark. I have heard that Bulls have been sighted in the Mississipi River as far north as Alton, IL. But there does seem to be a limit as to how long that they can tolerate fresh water. As there have been no confirmed sighting north of that, I’d say that’s the limit. And of course, the only way into the Great Lakes would seem to be the Saint Lawrence. And there have been locks there, so...