The Mississippi River Delta is the modern area of land built up by alluvium deposited by the Mississippi River as it slows down and enters the Gulf of Mexico. The deltaic process has, over the past 5,000 years, caused the coastline of south Louisiana to advance gulfward from 15 to 50 miles (24 to 80 km).
It is a biologically significant region, comprising 3 million acres (12,000 km²) of coastal wetlands and 40% of the salt marsh in the contiguous United States. It is also a commercially significant region, supporting the economy of New Orleans with significant shipping traffic, providing 16 to 18% of the oil supply in the U.S., and providing 16% of the fisheries harvest in the U.S., including shrimp, crabs, and crayfish.
The Mississippi River Delta is not to be confused with the Mississippi Delta region, an alluvial plain located some 300 miles (480 km) northward in western Mississippi along the river.