Ask NASA Climate | September 17, 2009, 17:00 PDT
Pick of the pics
This striking image is the result of silt, which appears blue as the Mississippi River flows off the southern coast of Louisiana and into the Gulf of Mexico. The brightness and shade of blue depends on the density of the silt and the depth of the silt-carrying currents in the water. The small bright dots in the scene are fishing boats and oil platforms. The picture was taken by NASA's Landsat 7 satellite on December 28, 2002.