Frozen Lake Sharpe, South Dakota - The Missouri River rises in the Rocky Mountains of western Montana, and flows generally to the southeast for 3,767 kilometers (2,341 miles) to its confluence with the Mississippi River north of St. Louis, Missouri. It is the longest river in North America. The river does not follow a straight southeasterly course along this distance, but includes many meander bends such as the one in this astronaut photograph from the International Space Station. This particular bend is occupied by Lake Sharpe, an approximately 130 kilometer (80 mile) long reservoir formed behind the Big Bend Dam on the Missouri River near Lower Brule, South Dakota. The lake surface is frozen and covered with snow, presenting a uniform white appearance. As meander bends develop, they tend to assume a distinctive U shape. Over time, the river channel can continue to cut into the ends of the “U,” eventually bringing them so close together that the river then cuts across the gap to achi...