The great American river under pressure
The Mississippi River is 3733 km long and runs from Lake Itasca to the Gulf of Mexico.
The Mississippi drains most of the area between the Rocky Mountains and the Appalachian Mountains, except for the areas drained by Hudson Bay via the Red River of the North, the Great Lakes and the Rio Grande.
Through a natural process known as delta switching the lower Mississippi River has shifted its final course to the ocean every thousand years or so. This occurs because the deposits of silt and sediment begin to clog its channel, raising the river's level and causing it to eventually find a steeper, more direct route to the Gulf of Mexico.
The abandoned distributary diminishes in volume and forms what are known as bayous. This process has, over the past 5,000 years, caused the coastline of south Louisiana to advance toward the Gulf from 25 to 80 km.
The Mississippi River has the third largest drainage basin in the world, exceeded in size only by the watersheds of the Amazon River and Congo River. It drains 41% of the US mainland.
Current threats
Conversion for agriculture, pollution in the form of sedimentation and pesticide contamination, and wastewater discharges from urban areas - pose major threats to the water quality of these rivers.
In addition, extensive hydrological modifications have destroyed the stream habitat for native fishes and other species, such as highly vulnerable native mussels.
