The Mississippi River is the largest river system in the United States and also the largest of North America. About 2,320 miles (3,730 km) long, the river originates at Lake Itasca, Minnesota and flows slowly southwards in sweeping meanders, terminating 95 river miles below New Orleans, Louisiana where it begins to flow to the Gulf of Mexico. Along with its major tributary, the Missouri River, the river drains all or parts of 31 U.S. states stretching from the Rocky Mountains in the west to the Appalachian Mountains in the east to the Canada-U.S. border on the north, including most of the Great Plains, and is the fourth longest river in the world and the tenth most powerful river in the world.

The current form of the Mississippi River basin was largely shaped by the Cordilleran Ice Sheet of the most recent Ice Age. The southernmost extent of this enormous glaciation extended well into the present-day United States and Mississippi basin. When the ice sheet began to recede, hundreds of feet of rich sediment were deposited, creating the flat and fertile landscape of the Mississippi Valley. During the melt, giant glacial rivers found drainage paths into the Mississippi watershed, creating such features as the Minnesota River, James River, and Milk River valleys. When the ice sheet completely retreated, many of these "temporary" rivers found paths to Hudson Bay or the Arctic Ocean, leaving the Mississippi Basin with many features "oversized" for the existing rivers to have carved in the same time period. The Mississippi River Delta has shifted and changed constantly since the formation of the river, but the construction of dams on the river has greatly reduced the flow of sediment to the delta. In recent years, the Mississippi's mouth has shown a steady shift towards the Atchafalaya River channel, but because of floodworks at the river's mouth, this change of course—which would be catastrophic for seaports at the river mouth—has been held at bay.

Hundreds of Native American tribes have depended on the Mississippi River and its tributaries for thousands of years. Although they knew the river by many different names, it was the Ojibwe word misi-ziibi, meaning Great River, or gichi-ziibi, meaning Big River, that ultimately gave the river its present-day name. European explorers reached the mouth of the river as early as the 1500s and 1600s. The river throughout history has served as the border for New France, New Spain, and the early United States—its size and importance made it a formidable boundary as well as a strategic military location, and later, an important artery for steamboats to travel on. Writer Mark Twain was one of the most well-known figures on the river in this period. Even today, the river serves as partial boundaries for ten states, and most of its course can easily be seen on a political map. The Mississippi has also been known for great flooding events, especially in the twentieth century which experienced up to four 100-year floods. This has led to the construction of hundreds of miles of levees along nearly the entire course of the river, although they have not always succeeded to prevent the greatest floods.

Throughout its history, whether for Native Americans, explorers, or modern commerce, the Mississippi has always been a major navigation route through the center of North America. In the 19th and 20th centuries, despite its slow current and relative depth, a series of dams were constructed on the river, one of the most notable of which is at St. Anthony Falls on the border between Minneapolis and St. Paul. These dams facilitate navigation for a steady stream of barge traffic carrying agricultural products from the fertile Mississippi Basin to the Gulf Coast, and like the Columbia River, most of the Mississippi also is a cascade of reservoirs. Most of its big tributaries—the Missouri and Ohio Rivers—have also been developed for navigation. However, the development of the 20th and 21st centuries has also come with environmental problems, the most infamous of which is the enormous Gulf of Mexico dead zone that extends hundreds of miles out to sea from the river's mouth. Because of dredging activity to deepen the Mississippi River channel, many natural features such as sandbars and meanders no longer exist. Efforts are being made to clean up the river and its tributaries, including the establishment of National Park Service sites on the river and the prevention of agricultural waste from flowing into the river.

From its origin at Lake Itasca to St. Louis, Missouri, the flow of the Mississippi River is moderated by 43 dams. Fourteen of these dams are located above Minneapolis in the headwaters region and serve multiple purposes including power generation and recreation. The remaining 29 dams beginning in downtown Minneapolis all contain locks and were constructed to permit commercial navigation of the upper river. Taken as a whole these 43 dams significantly shape the geography and influence the ecology of the upper river. Beginning just below Saint Paul, Minnesota and continuing throughout the upper and lower river, the Mississippi is further controlled by thousands of wing dikes that moderate the river's flow in order to maintain an open navigation channel and prevent the river from eroding its banks.

The Mississippi River runs through 10 states and was used to define portions of these states' borders. The middle of the riverbed at the time the borders were established was the line to define the borders between states. The river has since shifted, but the state borders of Wisconsin, Iowa, Illinois, Missouri, Kentucky, Arkansas, Tennessee, and Mississippi have not changed; they still follow the former bed of the Mississippi River as of their establishment.

The widest point of the Mississippi River is Lake Winnibigoshish, near Grand Rapids, Minnesota, at over 7 miles (11 km) across. Also of note is Lake Onalaska, near La Crosse, Wisconsin, where the river is over 4 miles (6.4 km) wide (created by Lock and Dam No. 7) and Lake Pepin at more than 2 miles (3.2 km) wide. However, the first two areas are lakes or reservoirs rather than free flowing water. In other areas where the Mississippi is a flowing river (other than Lake Pepin), it exceeds 1 mile (1.6 km) in width in several places in its lower course.

The Missouri River flows from the confluence of the Jefferson, Madison and Gallatin Rivers and is the longest river in the United States. Taken together, the Jefferson, the Missouri, and the Mississippi form the longest river system in North America. If measured from the source of the Jefferson at Brower's Spring, to the Gulf of Mexico, the length of the Mississippi-Missouri-Jefferson combination is approximately 3,900 miles (6,300 km), making the combination the 4th longest river in the world. The uppermost 207 miles (333 km) of this combined river are called the Jefferson, the lowest 1,352 miles (2,176 km) are part of the Mississippi, and the intervening 2,341 miles (3,767 km) are called the Missouri.

The Arkansas River is the second-longest tributary of the Mississippi River. Measured by water volume, the largest of all Mississippi tributaries is the Ohio River.

The source of the Upper Mississippi River is Lake Itasca, 1,475 feet (450 m) above sea level in Itasca State Park located in Clearwater County, Minnesota. The name "Itasca" is a combination of the last four letters of the Latin word for truth (veritas) and the first two letters of the Latin word for head (caput).

The uppermost lock and dam on the Mississippi River is the Upper St. Anthony Falls Lock and Dam in Minneapolis. Above the dam, the river's elevation is 799 feet (244 m). Below the dam, the river's elevation is 750 feet (230 m). This 49-foot (15 m) drop is the largest of all the Mississippi River locks and dams. The origin of the dramatic drop is a waterfall preserved adjacent to the lock under an apron of concrete. Saint Anthony Falls is the only true waterfall on the entire Mississippi River. The water elevation continues to drop steeply as it passes through the gorge carved by the waterfall. By the time the river reaches Saint Paul, Minnesota, below Lock and Dam #1, it has dropped more than half its original elevation and is 687 feet (209 m) above sea level. From St. Paul to St. Louis Missouri the river elevation falls much more slowly and is controlled and managed as a series of pools created by 26 locks and dams. From St. Louis to the Ohio River confluence, the Mississippi free falls a total of 220 feet (67 m) over a distance of 180 miles (290 km) for an average rate of 1.2 feet per mile (23 cm/km). At the Ohio River confluence the Mississippi is 315 feet (96 m) above sea level.

Tributaries

The Mississippi is joined by the Minnesota River south of the Twin Cities; the St. Croix River near Prescott, Wisconsin; the Black River (Mississippi River), La Crosse River, and Root River (Minnesota) in La Crosse, Wisconsin; the Wisconsin River in Prairie du Chien, Wisconsin; the Rock River in the Quad Cities; the Iowa River near Wapello, Iowa; the Skunk River south of Burlington, Iowa; the Des Moines River in Keokuk, Iowa; the Illinois River and the Missouri River near St. Louis; and by the Ohio River at Cairo, Illinois.

The Hennepin Canal roughly follows the ancient channel of the Mississippi downstream from Rock Island to Hennepin. South of Hennepin, Illinois, the current Illinois River is actually following the ancient channel of the Mississippi River to Alton, Illinois, before the Illinoian Stage.

Other changes in the course of the river have occurred because of earthquakes along the New Madrid Seismic Zone, which lies between Memphis and St. Louis. Three earthquakes in 1811 and 1812, estimated at approximately 8 on the Richter magnitude scale, were said to have temporarily reversed the course of the Mississippi. The settlement of Reverie, Tennessee was cut off from Tipton County, Tennessee, during the 1811 and 1812 earthquakes and placed on the western side of the Mississippi River, the Arkansas side. These earthquakes also created Reelfoot Lake in Tennessee from the altered landscape near the river. The faulting is related to an aulacogen (geologic term for a failed rift) that formed at the same time as the Gulf of Mexico.

Through a natural process known as delta switching, the lower Mississippi River has shifted its final course to the mouth of the Gulf of Mexico every thousand years or so. This occurs because the deposits of silt and sediment begin to clog its channel, raising the river's level and causing it to eventually find a steeper, more direct route to the Gulf of Mexico. The abandoned distributaries diminish in volume and form what are known as bayous. This process has, over the past 5,000 years, caused the coastline of south Louisiana to advance toward the Gulf from 15 to 50 miles (25–80 km). The currently active delta lobe is called the Birdfoot Delta, after its shape, or the Balize Delta, after La Balize, Louisiana, the first French settlement at the mouth of the Mississippi.

Native Americans

The area of the Mississippi valley was first settled by Native American tribes, such as the Cheyenne, Sioux, Ojibwe, Potawatomi, Ho-Chunk, Fox, Kickapoo, Tamaroa, Moingwena, Quapaw and Chickasaw.

The Cheyenne, one of the earliest inhabitants of the upper Mississippi River, called it the Máˀxe-éˀometaaˀe (Big Greasy River) in the Cheyenne language. However, the word Mississippi comes from Messipi, the French rendering of the Anishinaabe (Ojibwe or Algonquin) name for the river, Misi-ziibi (Great River).

The Ojibwe called Lake Itasca Omashkoozo-zaaga'igan (Elk Lake) and the river flowing out of it Omashkoozo-ziibi (Elk River). After flowing into Lake Bemidji, the Ojibwe called the river Bemijigamaag-ziibi (River from the Traversing Lake). After flowing into Cass Lake, the name of the river changes to Gaa-miskwaawaakokaag-ziibi (Red Cedar River) and then out of Lake Winnibigoshish as Wiinibiigoozhish-ziibi (Miserable Wretched Dirty Water River), Gichi-ziibi (Big River) after the confluence with the Leech Lake River, then finally as Misi-ziibi (Great River) after the confluence with the Crow Wing River. After the expeditions by Giacomo Beltrami and Henry Schoolcraft, the longest stream above the juncture of the Crow Wing River and Gichi-ziibi was named "Mississippi River". The Mississippi River Band of Chippewa Indians, known as the Gichi-ziibiwininiwag, are named after the stretch of the Mississippi River known as the Gichi-ziibi.

On May 8, 1541, Spanish explorer Hernando de Soto became the first recorded European to reach the Mississippi River, which he called Río del Espíritu Santo ("River of the Holy Spirit"), in the area of what is now Mississippi. In Spanish, the river is called Río Mississippi.

French explorers, Louis Jolliet and Jacques Marquette, began exploring the Mississippi in the 17th century. Marquette traveled with a Sioux named Ne Tongo ("Big river" in Sioux language) in 1673. Marquette proposed calling it the River of the Immaculate Conception.

In 1682, René-Robert Cavelier, Sieur de La Salle and Henri de Tonti claimed the entire Mississippi River Valley for France, calling the river Colbert River after Jean-Baptiste Colbert and the region La Louisiane, for King Louis XIV. On March 2, 1699, Pierre Le Moyne d'Iberville rediscovered the mouth of the Mississippi, following the death of La Salle. The French built the small fort of La Balise there to control passage.

Following Britain's victory in the Seven Years War the Mississippi became the border between the British and Spanish Empires. The Treaty of Paris (1763) gave Great Britain rights to all land east of the Mississippi and Spain rights to land west of the Mississippi. Spain also ceded Florida to Britain to regain Cuba, which the British occupied during the war. Britain then divided the territory into East and West Florida.

Article 8 of the Treaty of Paris (1783) states, "The navigation of the river Mississippi, from its source to the ocean, shall forever remain free and open to the subjects of Great Britain and the citizens of the United States". With this treaty, which ended the American Revolutionary War, Britain also ceded West Florida back to Spain to regain The Bahamas, which Spain had occupied during the war. Spain then had control over the river, south of 32°30' north latitude and in what is known as the Spanish Conspiracy, hoped to gain greater control of Louisiana and all of the west. These hopes ended when Spain was pressured into signing Pinckney's Treaty in 1795.

19th century

France reacquired 'Louisiana' from Spain in the secret Treaty of San Ildefonso in 1800. The United States bought the territory from France in the Louisiana Purchase of 1803. In 1815, the U.S. defeated Britain at the Battle of New Orleans, part of the War of 1812, securing American control of the river.

So many settlers traveled westward through the Mississippi river basin, as well as settled in it, that Zadok Cramer wrote a guide book called The Navigator, detailing the features and dangers and navigable waterways of the area. It was so popular that he updated and expanded it through 12 editions over a period of 25 years.

Civil War

20th century

The "Big Freeze" of 1918/19 blocked river traffic north of Memphis, Tennessee, preventing transportation of coal from southern Illinois. This resulted in widespread shortages, high prices, and rationing of coal in January and February.

In the spring of 1927, the river broke out of its banks in 145 places, during the Great Mississippi Flood of 1927 and inundated 27,000 sq mi (70,000 km²) to a depth of up to 30 ft (9.1 m).

On October 20, 1976, the automobile ferry, MV George Prince, was struck by a ship traveling upstream as the ferry attempted to cross from Destrehan, Louisiana, to Luling, Louisiana. Seventy-eight passengers and crew died, only eighteen survived the accident.

In 1988, record low water levels provided an opportunity and obligation to examine the climax of the wooden-hulled age. The Mississippi fell to 10 feet (3.0 m) below zero on the Memphis gauge. Four and a half acres of water craft remains were exposed on the bottom of the Mississippi River at West Memphis, Arkansas. They dated to the late 19th to early 20th centuries. The State of Arkansas, the Arkansas Archeological Survey, and the Arkansas Archeological Society responded with a two-month data recovery effort. The fieldwork received national media attention as good news in the middle of a drought.

The Great Flood of 1993 was another significant flood, primarily affecting the Mississippi above its confluence with the Ohio River at Cairo, Illinois.

Two portions of the Mississippi were designated as American Heritage Rivers in 1997: the lower portion around Louisiana and Tennessee, and the upper portion around Iowa, Illinois, Minnesota and Missouri.

In 2002, Slovenian long-distance swimmer, Martin Strel, swam the entire length of the river, from Minnesota to Louisiana, over the course of 68 days.

In 2005, the Source to Sea Expedition paddled the Mississippi and Atchafalaya Rivers to benefit the Audubon Society's Upper Mississippi River Campaign.^[20][21]

On August 1, 2007, the I-35W Mississippi River bridge in Minneapolis collapsed during the evening rush hour.