Frankly, I consider Bull Sharks far skarier than Great Whites. Unlike Great Whites, Bulls hunt in relatively shallow and murky water, where people swim.
They also go into rivers and ponds. (I'm pretty sure I say one in the bay in Southampton NY. (that would have done wonders for teh multi-million dollar waterfront estates.) No one believed me.
I doubt that too, but if one could get as far north as Alton, it wouldn't be hard for one to get into the Illinois River - which connects via the Cal-Sag Channel/DesPlaines River/Chicago River to Lake Michigan. Stranger things have happened.