That certainly seems to be the case here, but it's true that bull sharks have been found as far north up the Mississippi as Cairo, Illinois, having swum up from the gulf. They've been found up to 4,000 km inland up the Amazon, and are quite tolerant of freshwater. They're not uncommon here (Louisiana) in the brackish to fresh waters of the Atchafalaya basin, and after Katrina, a number were observed in Lake Pontchartrain.
Oh, my. It's really only about 120 miles to the Arch from there.
Just last night we watched a re-run of River Monsters and the episode was tracking Bull Sharks in the Breede River in South Africa. They had travelled many miles upstream and there were quite a few of them, one they caught to track was the biggest Bull Shark known. Interesting, not very comforting that they supposedly don’t usually attack people.