river, principal river of the United States, c.2,350 mi (3,780 km) long, exceeded in length only by the Missouri, the chief of its numerous tributaries. The combined Missouri-Mississippi system (from the Missouri's headwaters in the Rocky Mts. to the mouth of the Mississippi) is c.3,740 mi (6,020 km) long and ranks as the world's third longest river system after the Nile and the Amazon. With its tributaries, the Mississippi drains c.1,231,000 sq mi (3,188,290 sq km) of the central United States, including all or part of 31 states and c.13,000 sq mi (33,670 sq km) of Alberta and Saskatchewan in Canada. Cotton and rice are important crops in the lower Mississippi valley; sugarcane is raised in the delta. The Mississippi is abundant in freshwater fish; shrimp are taken from the briny delta waters. The delta also yields sulfur, oil, and gas.
The Mississippi River rises in small streams that feed Lake Itasca (alt. 1,463 ft/446 m) in N Minnesota and flows generally south to enter the Gulf of Mexico through a huge delta in SE Louisiana. A major economic waterway, the river is navigable from the sediment-free channel maintained through South Pass in the delta to the Falls of St. Anthony in Minneapolis, with canals circumventing the rapids near Rock Island, Ill., and Keokuk, Iowa. For the low-water months of July, August, and September, there is a 45-ft (13.7-m) channel navigable by oceangoing vessels from Head of the Passes to Baton Rouge, La., and a 9-ft (2.7-m) channel from Baton Rouge deep enough for barges and towboats to Minneapolis. The Mississippi connects with the Intracoastal Waterway in the south and with the Great Lakes–St. Lawrence Seaway system in the north by way of the Illinois Waterway.
Along the river's upper course shipping is interrupted by ice from December to March; thick, hazardous fogs frequently settle on the cold waters of the unfrozen sections during warm spells from December to May. In its upper course the river is controlled by numerous dams and falls c.700 ft (210 m) in the 513-mi (826-km) stretch from Lake Itasca to Minneapolis and then falls c.490 ft (150 m) in 856 mi (1,378 km) from Minneapolis to Cairo, Ill. The Mississippi River receives the Missouri River 17 mi (27 km) N of St. Louis and expands to a width of c.3,500 ft (1,070 m); it swells to c.4,500 ft (1,370 m) at Cairo, where it receives the Ohio River. The stretch of the river from the last dam and locks, above St. Louis, to Cairo is also known as the middle Mississippi.
The lower Mississippi meanders in great loops across a broad alluvial plain (25–125 mi/40–201 km wide) that stretches from Cape Girardeau, Mo., to the delta region S of Natchez, Miss. The plain is marked with oxbow lakes and marshes that are remnants of the river's former channels. Natural levees, built up from sediment carried and deposited in times of flood, border the river for much of its length; sediment has also been deposited on the riverbed, so that in places the surface of the Mississippi is above that of the surrounding plain, as evidenced by the St. Francis, Black, Yazoo, and Tensas river basins. Breaks in the levees frequently flood the fertile bottomlands of these and other low-lying areas of the plain.
After receiving the Arkansas and Red rivers, the Mississippi enters a birdsfoot-type delta, which was built outward by sediment carried by the main stream since c.A.D. 1500 It then discharges into the Gulf of Mexico through a number of distributaries, the most important being the Atchafalaya River and Bayou Lafourche. The main stream continues southeast through the delta to enter the gulf through several mouths, including Southeast Pass, South Pass, and Pass à Loutre. Indications that the Mississippi River might abandon this course and divert through the Atchafalaya River led to the construction of a series of dams, locks, and canals by the U.S. Army Corps of Engineers. Known as the Old River Control Structure, it was undertaken to prevent such an occurrence. Sluggish bayous and freshwater lakes (such as Pontchartrain, Grand, and Salvador) dot the delta region.
Regarding the delta, environmentalists and those in the seafood industry are concerned by the loss of 25–45 sq mi (65–104 sq km) of marsh a year; fish and wildlife populations are threatened as their natural habitat slowly disappears. The loss has been attributed to subsidence and a decrease in sediment largely due to dams, artificial channeling, and land conservation measures. Pollution and the cutting of new waterways for petroleum exploration and drilling have also taken their toll on the delta. Louisiana has enacted environmental protection laws that are expected to slow, but not halt, the loss of the delta marshes.
The flow of the river is greatest in the spring, when heavy rainfall and melting snow on the tributaries (especially the Missouri and the Ohio) cause the main stream to rise and frequently overflow its banks and levees, inundating vast areas of the plain. Since the disastrous flood of 1927 the U.S. Congress has authorized the construction of dams on the upper Mississippi and its tributaries to regulate the flow; the building of c.1,600 mi (2,580 km) of levees below Cape Girardeau to contain the swollen river; and the establishment of floodways to divert water at critical points, such as the Cairo–New Madrid, Atchafalaya, and Morganza floodways and the Bonnet Carre Spillway at New Orleans, which diverts water into Lake Pontchartrain. Cutoffs have eliminated the dangerous winding channels, and an improved main channel has increased the river's flood-carrying capacity. A 220-acre (89-hectare) model of the Mississippi River basin is located at Clinton, Miss., which has been used by the U.S. Corps of Engineers to simulate various conditions in the basin.
Nonetheless, serious, record-breaking floods again occurred in the rainy spring of 1973, when the river crested at St. Louis at 43.3 ft (13.2 m), and again in the summer of 1993, when the river crested at St. Louis at 49.6 ft (15.1 m), killing 50 people, displacing 50,000, and causing $12 billion in agricultural and property damage. In the spring of 2011, heavy rains in April in the S central Mississippi river basin led to near-record high water and flooding from parts of Missouri and Illinois south. The narrow river channel that has been created by building levees has worsened flooding in some instances.
In 1988 a severe drought brought water levels down to their lowest point in recorded history and halted most river traffic. Severe drought again threatened to halt traffic in the middle Mississippi in 2012–13, but dredging and other channel deepening measures kept the river open.
The Spanish explorer Hernando De Soto is credited with the European discovery of the Mississippi River in 1541. The French explorers Jacques Marquette and Louis Jolliet reached it through the Wisconsin River in 1673, and in 1682 La Salle traveled down the river to the Gulf of Mexico and claimed the entire territory for France. The French founded New Orleans in 1718 and effectively extended control over the upper river basin with settlements at Cahokia, Kaskaskia, Prairie du Chien, and St. Louis. France ceded the river to Spain in 1763 but regained it in 1800; the United States acquired the Mississippi River as part of the Louisiana Purchase in 1803.
A major artery for the Native Americans and the fur-trading French, the river became in the 19th cent. the principal outlet for the newly settled areas of mid-America; exports were floated downstream with the current, and imports were poled or dragged upstream on rafts and keelboats. The first steamboat plied the river in 1811, and successors became increasingly luxurious as river trade increased in profitability and importance; the era is colorfully described in Mark Twain's Life on the Mississippi (1883).
Traffic from the north ceased after the outbreak of the Civil War. During the Civil War the Mississippi was an invasion route for Union armies and the scene of many important battles. Especially decisive were the capture of New Orleans (1862) by Adm. David Farragut, the Union naval commander, and the victory of Union forces under Grant at Vicksburg in 1863. River traffic resumed after the war, but much of the trade was lost to the railroads. With modern improvements in the channels of the river there has been a great increase in traffic, especially since the mid-1950s, with principal freight items being petroleum products, chemicals, sand, gravel, and limestone.
- See The Mighty Mississippi (1971). ,
- Great River: An Environmental History of the Upper Mississippi (1985). ,
- Smart, M. M., et al. Ecological Perspectives of the Upper Mississippi River (1986).
- Rising Tide: The Great Mississippi Flood of 1927 and How It Changed America (1997). ,
- The Big Muddy (2012). ,
- Old Man River (2013). ,
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