Bull sharks are remarkably tolerant of fresh water, and are found in Lake Nicaragua, up various rivers, the Chesapeake Bay, etc...
Watch the program called “River Monsters” on bull sharks, they provided significant evidence that they can breed in fresh water as well.
In Australia there is a river which is blocked by a relatively low dam. Back in the 80’s (I believe) it went underwater from massive floods. Well now there are bull sharks both large and small living above the dam. The small sharks pretty much had to have been born in fresh water.