Supposedly a fisherman and a friend spotted a Bull Shark in the Chattahoochee river near Columbus, Georgia yesterday. More details here
It's probably a hoax but there is still a chance it could be true. Bull Sharks have been found in rivers as far inland as Indiana! There are even Bull sharks living in Lake Nicaragua! So just because you're in a lake or river, you're not 100% safe from sharks. Bull sharks are very aggressive, extremely territorial and are among the three species most likely to attack humans.