| Lower Mississippi River | |
|---|---|
 35 barges passing under theVicksburg Bridge byVicksburg, Miss. | |
| Location | |
| Country | US |
| Physical characteristics | |
| Source | |
| • location | Cairo,Illinois (confluence ofOhio River and theMiddle Mississippi River) |
| • elevation | 315 ft (96 m) |
| Mouth | |
• location | Gulf of Mexico |
| Length | 1,600 km (990 mi) |
TheLower Mississippi River is the portion of theMississippi River downstream ofCairo,Illinois. From theconfluence of theOhio River and theMiddle Mississippi River at Cairo, the Lower flows just under 1000 miles (1600 km) to theGulf of Mexico.[1] It is the most heavily travelled component of theMississippi River System.[2]
Unlike on the upper rivers, there are nolocks ordams on the Lower Mississippi. The river is, however, constrained bylevees anddikes to control flooding and secure a navigation channel forbarges.[3] TheOld River Control Structure, theBonnet Carré Spillway, theMississippi River – Gulf Outlet Canal and other man-made structures on the lower reaches of the river seek to manipulate the flow of water in the vicinity ofNew Orleans.[4]
The political and engineering focus in the 20th century was to separate the Lower Mississippi River from itsfloodplain. Levees andchannelization—along with substantial loss of bottomland forests to agriculture in thealluvial valley—have resulted in a loss of wildlife and fish habitat, decreased water quality, and an expansion of thehypoxic zone in theGulf of Mexico. Agriculturalrunoff has resulted in increasedturbidity,siltation, pollution frompesticides,toxicity to aquatic organisms, oxygen depletion andeutrophication.[5]
Channel depth of 9 feet is maintained by theCorps of Engineers fromSt. Louis, Missouri toBaton Rouge, Louisiana.
On the Lower Mississippi, from Baton Rouge to the Gulf, the navigation depth is 45 feet, allowing for container ships and cruise ships to dock at thePort of New Orleans and bulk cargo ships shorter than 150 foot air draft to fit under theHuey P. Long Bridge and traverse the Mississippi to Baton Rouge.[7] There is afeasibility study to dredge this portion of the river to 50 feet to allowNew Panamax ship depths.[8]
