The Mississippi is not so much a river as a drainage system the size of India. From its conventional source at Lake Itasca in northern Minnesota, the main stem runs 3,766 kilometres to the Gulf of Mexico south of New Orleans. Along the way it picks up the Missouri (from the Rocky Mountains in Montana), the Ohio (from the Appalachian Mountains in Pennsylvania), the Arkansas (from the southern Rockies), the Red (from Texas and Louisiana), the Tennessee, the Yazoo, and dozens of smaller rivers. Together the system drains approximately 41 percent of the contiguous United States — about 3.2 million square kilometres — and produces an average discharge at the mouth of around 17,000 cubic metres per second, fifth largest in the world. About a third of all the freight that moves in the United States by waterway moves on this system. Mark Twain spent his most productive years writing about it. It floods catastrophically every few decades, and the engineering that has been built to control it is among the largest civil-engineering programmes ever undertaken anywhere.
The Three Reaches
The river is conventionally divided into three reaches with distinct characters. The Upper Mississippi runs from Lake Itasca to St Louis, Missouri, where the Missouri joins. Through Minnesota, Wisconsin, Iowa, and Illinois, the Upper Mississippi is a series of artificial pools created by 29 locks and dams built in the 1930s by the Army Corps of Engineers, primarily for barge navigation. The Middle Mississippi, from St Louis to the confluence with the Ohio at Cairo, Illinois, is the deeper unimpounded section. The Lower Mississippi, from Cairo to the Gulf, is the broadest and most heavily engineered section — the great floodplain river that gives the system its character. Below St Louis, no dams cross the main stem.
The Levees
The defining feature of the Lower Mississippi is the levee system that confines it. The river's natural floodplain in the lower reaches is up to 200 kilometres wide; the river's normal channel uses only a small fraction of that space. The levees — built up over more than a century by federal, state, and local agencies — confine the river to a channel typically 1-2 kilometres wide along most of its lower course, with riverside towns and cities (Memphis, Vicksburg, Baton Rouge, New Orleans) sitting behind levees that hold back water higher than the surrounding land. The system works, mostly. When it fails, it fails catastrophically. The 1927 Great Mississippi Flood overtopped the levees in dozens of places, inundated 70,000 km², killed several hundred people, and forced the migration of hundreds of thousands. The 1993 flood was a similar event further north. The 2011 flood approached comparable levels but was managed by deliberately opening a series of spillways that diverted water away from major cities, including a controversial flooding of agricultural land in Missouri and Louisiana to spare Cairo and New Orleans.
Mark Twain
Samuel Clemens — Mark Twain — was born in Florida, Missouri, in 1835 and grew up in Hannibal, on the Mississippi north of St Louis. He worked as a steamboat pilot on the river from 1857 to 1861, and the pen name "Mark Twain" comes from the leadsman's call for two fathoms of depth — safe water — when sounding the river bottom. Twain's books — particularly Life on the Mississippi, The Adventures of Tom Sawyer, and The Adventures of Huckleberry Finn — created the dominant literary image of the river for the English-speaking world. Hannibal today is a small tourist town that has built much of its modern economy around the Twain legacy. The literary Mississippi of Tom Sawyer and Huck Finn — leisurely, slightly dangerous, populated by characters at the margins of respectability — was not quite the actual Mississippi even in Twain's lifetime, but it has remained the dominant cultural Mississippi for over a century.
New Orleans
New Orleans sits in a remarkable geographic position: on the natural levee of the Mississippi at the head of the river's delta, surrounded on three sides by water (the river, Lake Pontchartrain to the north, and the bayou-and-swamp country of southeast Louisiana). The city was founded by the French in 1718 on slightly higher ground that the river's natural deposits had built up. The land between the river and the lake is mostly below sea level — some of it 1-3 metres below — and is kept dry by a system of levees and pumps that has been progressively expanded since the early 20th century. The 2005 failure of the levee system during Hurricane Katrina flooded 80 percent of the city and killed approximately 1,400 people. The post-Katrina reconstruction has rebuilt most of the city, with substantial federal investment in the levee and flood-protection system, though the underlying geography remains as challenging as ever and the city's long-term vulnerability to a combination of subsidence and sea-level rise is not in dispute among engineers.
The Atchafalaya Problem
One of the slow-motion problems of the Lower Mississippi is the threat that the river will simply choose a different route to the sea. The Atchafalaya River, which branches off the Mississippi about 300 kilometres above New Orleans, is steeper, shorter, and more direct to the Gulf than the Mississippi's current course past Baton Rouge and New Orleans. Without intervention, the Mississippi would have transferred its main flow to the Atchafalaya channel some time in the 1970s. The transfer is being prevented by the Old River Control Structure, a complex of gates and levees built by the Army Corps of Engineers in the 1950s and 1960s, which limits the amount of Mississippi water diverted into the Atchafalaya and forces the rest to continue down the established channel past Baton Rouge. The Old River Control Structure nearly failed during the 1973 flood and has been progressively reinforced since. If it ever does fail, the Mississippi will reroute itself, leaving New Orleans on a dramatically reduced river and the Atchafalaya basin with a much larger one.
Barge Traffic and Agriculture
The Mississippi system is the backbone of bulk commodity movement in the central United States. Grain (corn, soybeans, wheat), coal, petroleum products, fertiliser, and steel move by barge along the river and its tributaries in volumes that would require many millions of additional truck trips per year if the river were not navigable. A typical "15-barge tow" — one towboat pushing 15 connected barges — carries the equivalent of about 870 truck loads. The Port of South Louisiana, at the lower end of the river above New Orleans, is by some measures the largest port in the United States by tonnage handled. The economics of American agriculture in the Midwest depend substantially on the river as a low-cost route for grain exports.
The Dead Zone
The agricultural drainage that reaches the Gulf of Mexico via the river produces a seasonal "dead zone" of low-oxygen water near the Mississippi mouth each summer. Fertiliser runoff (nitrogen and phosphorus) feeds algal blooms in the warm summer waters; the bacteria that decompose the algae consume oxygen, leaving the water uninhabitable for most fish and shellfish. The dead zone reached a maximum of nearly 23,000 km² in 2017 and is conventionally one of the largest in the world. Reducing it would require substantial changes in agricultural practice across a basin that contains a third of the country's farmland — a political project that has been discussed for decades without producing meaningful change.
Music and the River
The Mississippi has been central to the development of American popular music to an unusual degree. The Delta blues — the foundational genre of 20th-century American popular music — emerged in the cotton-growing Mississippi Delta region of northwest Mississippi in the early 20th century. Robert Johnson, Charley Patton, Son House, and Muddy Waters all played in the small Delta towns along Highway 61 that runs parallel to the river. The blues migrated north with Black Americans during the Great Migration to St Louis, Memphis, Chicago, and Detroit, evolving in each city into the genres that would later produce rock and roll. The river itself appears as a character in dozens of significant American songs (from Paul Robeson's "Ol' Man River" to Johnny Cash's "Big River" to John Hartford's "Gentle on My Mind"), and the river towns — particularly Memphis and New Orleans — have produced disproportionate numbers of significant musicians for over a century.
The Long View
The Mississippi has been engineered more thoroughly than any other major river in the world. The levees confine its flow. The dams regulate its upper reaches. The Old River Control Structure determines its lower path. The cities along its banks depend on the engineering working as designed. Whether all of this can be maintained indefinitely under conditions of more intense rainfall, slow subsidence of the delta, and continued sea-level rise is genuinely uncertain. The river has flooded catastrophically on average every few decades for the entire period of European settlement. The next flood will, eventually, exceed the design capacity of the levees at some specific location, and the city or agricultural district behind that location will pay the price. Engineering the Mississippi is not a finished project. It is a continuous one, and the river has not lost a long enough run of contests to make anyone confident about the outcome.