<Tr> <Th_colspan="2"> National Wild and Scenic River </Th> </Tr> <Tr> <Th> Type </Th> <Td> Wild, Scenic, Recreational </Td> </Tr> <P> The Missouri River is the longest river in North America . Rising in the Rocky Mountains of western Montana, the Missouri flows east and south for 2,341 miles (3,767 km) before entering the Mississippi River north of St. Louis, Missouri . The river takes drainage from a sparsely populated, semi-arid watershed of more than half a million square miles (1,300,000 km), which includes parts of ten U.S. states and two Canadian provinces . When combined with the lower Mississippi River, it forms the world's fourth longest river system . </P> <P> For over 12,000 years, people have depended on the Missouri River and its tributaries as a source of sustenance and transportation . More than ten major groups of Native Americans populated the watershed, most leading a nomadic lifestyle and dependent on enormous bison herds that once roamed through the Great Plains . The first Europeans encountered the river in the late seventeenth century, and the region passed through Spanish and French hands before finally becoming part of the United States through the Louisiana Purchase . The Missouri was long believed to be part of the Northwest Passage--a water route from the Atlantic to the Pacific--but when Lewis and Clark became the first to travel the river's entire length, they confirmed the mythical pathway to be no more than a legend . </P>

What body of water does the missouri river empty into