Mississippi River, chief river of the North American continent and the longest river in the United States, flowing about 2,350 mi (3,780 km) south from Lake Itasca in northwestern Minnesota to its enormous delta at the Gulf of Mexico, below New Orleans. Called the “father of waters” by Native Americans, the Mississippi drains an area of about 1.25 million sq mi (3,237,500 sq km). With the Missouri and Ohio rivers (its chief tributaries), it forms the world's third longest river system, after the Nile and the Amazon. It receives more than 250 tributaries in all. The Mississippi is noted for sudden changes of course, its length varying by 40–50 mi (64–80 km) per year. The river's average discharge is 1.64 million cu ft (46,412 cu m) per sec, but in high water season this soars to some 2.3 million cu ft (65,090 cu m) per sec. Hooding is a serious problem, but dikes and levees contain its periodic massive overflows. The river is a major transportation artery of the United States and was of fundamental importance in the development of the North American continent.