"Unlike most sharks, bull sharks tolerate fresh water and can travel far up rivers. They have even been known to travel as far up as Indiana in the Ohio River and Illinois in the Mississippi River, although there have been few recorded attacks. As a result, they are probably responsible for the majority of near-shore shark attacks, including many attacks attributed to other species.[3] However, bull sharks are not true freshwater sharks "
http://en.wikipedia.org/wiki/Bull_shark
Notably there in the top 3 for attacking humans...
