The largest river system in North America. About 2,320 miles (3,730 km) long, the river originates at Lake Itasca, Minnesota, and flows slowly southwards in sweeping meanders, terminating 95 miles (153 km) by river below New Orleans, where it begins to flow to the Gulf of Mexico. Along with its major tributary, the Missouri River, the river drains all or parts of 31 U. S. States stretching from the Rocky Mountains in the west to the Appalachian Mountains in the east to the Canada–US border on the north, including most of the Great Plains, and ( is the fourth longest river in the world and the tenth most powerful river in the world).