The Mississippi River, derived from the old Ojibwe word misi-ziibi meaning 'great river' (gichi-ziibi 'big river' at its headwaters), is the second-longest named river in North America, with a length of 2320 miles (3733 km) from Lake Itasca to the Gulf of Mexico. The longest named river in North America is its tributary, the Missouri River, with a length of 2341 miles (3767 km) from the confluence of the Jefferson, Madison, and Gallatin to the Mississippi River. Taken together, the Jefferson, Missouri, and Mississippi form the largest river system in North America.

If measured from the source of the Jefferson to the Gulf of Mexico, the length of the Mississippi-Missouri-Jefferson combination is approximately 3900 miles (6275 km), making the combination the 3rd longest river in the world. The uppermost 207 mi (333 km) of this combined river are called the Jefferson, the lowest 1352 mi (2175 km) are part of the Mississippi, and the intervening 2341 mi (3767 km) are called the Missouri.

Apart from the Missouri, the longest of the many long Mississippi tributaries is the Arkansas River. Measured by water volume, the largest of all Mississippi tributaries is the Ohio River.

Geography

See also: Mississippi River Delta

the source of the Mississippi River is on the edge of Lake Itasca. With its source Lake Itasca at 1,475 feet (450 m) above sea level in Itasca State Park located in Clearwater County, Minnesota, the river falls to 725 feet (220 m) just below Saint Anthony Falls in Minneapolis, the only waterfall along the river's course. The Mississippi is joined by the Minnesota River in Minneapolis, Minnesota, the Illinois River and the Missouri River near St. Louis, Missouri, and by the Ohio River at Cairo, Illinois. The Arkansas River joins the Mississippi in the state of Arkansas. The Atchafalaya River in Louisiana is a major distributary of the Mississippi.

The Mississippi drains most of the area between the Rocky Mountains and the Appalachian Mountains, except for the areas drained by Hudson Bay via the Red River of the North, the Great Lakes and the Rio Grande. It runs through two states — Minnesota and Louisiana — and was used to define the borders of eight states (the river has since shifted, but the state borders have not) — Wisconsin, Iowa, Illinois, Missouri, Kentucky, Arkansas, Tennessee, and Mississippi — before emptying into the Gulf of Mexico about 100 miles (160 km) downstream from New Orleans. Measurements of the length of the Mississippi from Lake Itasca to the Gulf of Mexico vary, but the EPA's number is 2,320 miles (3,733 km). The retention time from Lake Itasca to the Gulf is about 90 days.

Source:  www.wikipedia.com