Lower Mississippi River

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Lower Mississippi River
The Lower Mississippi River Towboats, barges and ships near New Orleans.
Origin	Cairo, Illinois (confluence of Ohio River and Upper Mississippi River)
Mouth	Gulf of Mexico
Basin countries	US
Length	1600 km (1000 mi)
Source elevation	96 m (315 ft)

Main article: Mississippi River

The Lower Mississippi River is the portion of the Mississippi River downstream of Cairo, Illinois. From the confluence of the Ohio River and Upper Mississippi River at Cairo, the Lower flows just under 1600 kilometers (1000 mi) to the Gulf of Mexico.^[1] It is the most heavily travelled component of the Mississippi River System.^[2]

Unlike on the upper rivers, there are no locks or dams on the Lower Mississippi. The river is, however, constrained by levees and dikes to control flooding and secure a navigation channel for barges.^[3] The Old River Control Structure, the Bonnet Carré Spillway, and other man-made structures on the lower reaches of the river seek to manipulate the flow of water in the vicinity of New Orleans.^[4]

The political and engineering focus in the 20th century was to separate the Lower Mississippi River from its floodplain. Levees and channelization—along with substantial loss of bottomland forests to agriculture in the alluvial valley—have resulted in a loss of wildlife and fish habitat, decreased water quality, and an expansion of the hypoxic zone in the Gulf of Mexico. Agricultural runoff has resulted in increased turbidity, siltation, pollution from pesticides, toxicity to aquatic organisms, oxygen depletion and eutrophication.^[5]