Louisiana's Coastal Area - Ecosystem Restoration The Louisiana coastal plain remains the largest expanse of coastal wetlands in the contiguous United States. The coastal wetlands, built by the land building or "deltaic" processes of the Mississippi River, contain an extraordinary diversity of estuarine habitats that range from narrow natural levee and beach ridges to expanses of forested swamps and fresh, brackish, and saline marshes. Taken as a whole, the unique interplay of habitats — with their hydrological connections to each other, upland areas, the Gulf of Mexico, and migratory routes of birds, fish, and other species — combines to place the coastal wetlands of Louisiana among the Nation’s most productive and important natural assets.