section_path: Navigation and flood control
section_name: Navigation and flood control
paragraph_text: Navigation and flood control
  
  A clear channel is needed for the barges and other vessels that make the main stem Mississippi one of the great commercial waterways of the world. The task of maintaining a navigation channel is the responsibility of the United States Army Corps of Engineers, which was established in 1802. Earlier projects began as early as 1829 to remove snags, close off secondary channels and excavate rocks and sandbars.
  
  The upper backwaters of the Mississippi normally freeze over by December, while the main channel freezes over only in the coldest years, historically as far south as St. Louis.
  
  A series of 29 locks and dams on the upper Mississippi, most of which were built in the 1930s, is designed primarily to maintain a 9-foot-deep (2.7 m) channel for commercial barge traffic. The lakes formed are also used for recreational boating and fishing. The dams make the river deeper and wider but do not stop it. No flood control is intended. During periods of high flow, the gates, some of which are submersible, are completely opened and the dams simply cease to function. Below St. Louis, the Mississippi is relatively free-flowing, although it is constrained by numerous levees and directed by numerous wing dams. The scope and scale of the levees, built along either side of the river to keep it on its course, has often been compared to the Great Wall of China.
  
  On the lower Mississippi, from Baton Rouge to the mouth of the Mississippi, the navigation depth is 45 feet (14 m), allowing container ships and cruise ships to dock at the Port of New Orleans and bulk cargo ships shorter than 150-foot (46 m) air draft that fit under the Huey P. Long Bridge to traverse the Mississippi to Baton Rouge. There is a feasibility study to dredge this portion of the river to 50 feet (15 m) to allow New Panamax ship depths.