Yes Bull sharks are known to live in freshwater rivers. They travel up the rivers from the ocean, and can be found hundreds of miles upstream. They are one of the most aggressive sharks, with an extremely high level of testosterone. But shark attacks are rare on humans. I dont know the statistics, but I have never heard of a shark attack in a river. I live in FL, and usually shark attacks happen in the ocean at dawn and dusk (feeding time). So if you are going to swim in the river, make sure you dont during dawn and dusk. I wouldnt worry other than that. It is highly unlikely you will get attacked by a shark.