The Bull shark is found in tropical and subtropical coastal waters worldwide as well as in many river systems and some freshwater lakes. They have been reported 3700 km (2220 miles) up the Amazon River in Peru, and over 3000 km (1800 miles) up the Mississippi River in Illinois. A group of Bull sharks found in Lake Nicaragua (Central America) was once thought to be landlocked, but they found access to the ocean through rivers and estuaries. In the western Atlantic Bull sharks migrate north along the coast of the U.S during summer, swimming as far north as Massachusetts, and then return to tropical climates when the coastal waters cool.