English: The Mississippi River flows more than 2,300 miles (3,700 km) from Lake Itasca in northern Minnesota to the Gulf of Mexico, draining parts of 31 U.S. states and two Canadian provinces along the way. After winding southward across the United States—and collecting copious sediment—the Mighty (and muddy) Mississippi slows its speed in southern Louisiana, ultimately dumping sediment across the expansive Mississippi Delta at the terminus of its journey.

The large “Birdsfoot Delta” formed by the deposition of sediment from the Mississippi (and so named for its birds-foot like shape) has expanded over time to nearly reach the continental shelf, bringing the edge of the shipping channels very close to deep water. This provides excellent opportunity for commerce and transportation, giving rise to thriving port cities, such as New Orleans.

River deltas have a natural life cycle of deposition and enlargement followed by some degree of truncation and shrinkage. As a river delta grows longer, the resistance to free flow of water tends to increase. The flowing water then seeks a channel of lower resistance, typically a minor tributary of the original river. As this tributary carries more and more water and sediment, it then begins to build a delta of its own while the original delta, now starved for water flow and sediment while facing forces of erosion, tends to shrink.

This scenario is being played out in Louisiana where the Atchafalaya River, a tributary of the Mississippi River, is expanding its deltas into the Atchafalaya Bay while the Mississippi Delta is shrinking. The loss of land in the Mississippi Delta has been estimated at nearly 5,000 square kilometers (2,000 square miles) from 1927 – 2017. To put it in another way, that’s as if most of Delaware had sunk into the sea over an 80-year period. Experts say this loss is due to more than natural cycling of deltas. Rising sea level, levees built to control and divert water flow, the incursion of salt water (which kills marsh plants) due to cutting new shipping lanes, changing coastal hydrology in support of expanding gas and oil industries, and upriver dams all impact the health and size of the Mississippi River Delta.

The Moderate Resolution Imaging Spectroradiometer (MODIS) on board NASA’s Terra satellite acquired a true-color image of the Mississippi River Delta on November 18, 2018. A large plume of tan sediment surrounds the “Birdsfoot Delta” in the lower right (southeast) section of the image. In the west (left), the Atchafalaya River pours heavy sediment into the Atchafalaya Bay.