I want to say that the bull shark is the top freshwater predator. They can live in salt and freshwater. Eventhough they aren't considered true freshwater fish, they are considered one of the most dangerous sharks because they can live in freshwater rivers and they are usually in shallow waters. Imagine swimming in a freshwater river and getting attacked by a big shark!!!
This is what wikipedia says," The bull shark, Carcharhinus leucas, also known as the bull whaler, Zambezi shark or informally Zambi in Africa and Nicaragua shark in Nicaragua, is common worldwide in warm, shallow waters along coasts and in rivers. The bull shark is well known for its unpredictable, often aggressive behavior. Many scientists agree that since bull sharks often dwell in shallow waters, they may be more dangerous to humans than any other species of sharks.[1] Unlike most other marine sharks, bull sharks tolerate fresh water. They can travel far up rivers. As a result, they are probably responsible for the majority of shark attacks on humans that take place near the shore, including many attacks attributed to other species.[2] However, bull sharks are not true freshwater sharks (unlike the river sharks of the genus Glyphis)."