The Mississippi River Delta is formed by the accumulation of sediment at the river's mouth. The turbid, nutrient-rich waters enter the Gulf of Mexico, where, every summer, one of the world's largest "dead zones" appears off the coasts of Louisiana and Texas.

This expanse of low-oxygen, or hypoxic, waters is produced by an overgrowth of algae caused by high nutrient concentrations. When the algae die and sink, bacteria consume them and consume the available oxygen, rendering the area uninhabitable.

Last year, the Gulf of Mexico dead zone was estimated at a record 8,800 square miles--about the size of New Jersey. The Advanced Spaceborn Thermal Emission and Reflection Radiometer (ASTER) instrument on the Terra satellite captured this image.