Mississippi River System
From the perspective of natural geography and hydrology, the system consists of the Mississippi River itself and its numerous natural tributaries and distributaries. The major tributaries are the Ohio, Illinois, Arkansas, Red and Missouri Rivers and, indirectly, such major Ohio River tributaries as the Allegheny, Tennessee, and Wabash rivers. 
From the perspective of modern commercial navigation, the system includes the above as well as navigable inland waterways which are connected by artificial means. Important connecting waterways include the Illinois Waterway, the Tennessee-Tombigbee Waterway, and the Gulf Intracoastal Waterway. This system of waterways is maintained by the U.S. Army Corps of Engineers with a project depth of between 9 and 12 feet (2.7 – 3.7 m) to accommodate barge transportation, primarily of bulk commodities. 
The Mississippi River carries 60% of U.S grain shipments, 22% of oil and gas shipments, and 20% of coal.
- "Mississippi River". USGS Biological Resources. Archived from the original on 2005-10-28. Retrieved 2006-03-08.
- "The Mississippi River System". US Army Corps of Engineers. Retrieved 2006-03-08.
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