Turbid waters from the third-longest river system in the world spill out into the Gulf of Mexico where their suspended sediment is deposited to form the Mississippi River Delta. Like the webbing on a duck's foot, marshes and mudflats in this 2001 satellite photo prevail between the shipping channels that have been cut into the delta. The deltaic progression has advanced South Louisiana's coastline 25-80 km (15-50 mi) over 5,000 years. In 2005, Hurricanes Rita and Katrina destroyed much of the delta and rising sea levels have increased erosion. Image courtesy of USGS.