Graphic comparing three images of the U.S. National Mall. thumbnail: http://svs.gsfc.nasa.gov/vis/a010000/a010800/a010873/AB-National_Mall_image_gal.png

Above the Earth, Below the Surface: Landsat’s Role in Monitoring Water Quality
Safeguarding freshwater resources is crucial, and while scientists use a variety of ground-based techniques to gauge water quality, the Landsat program has provided water quality data from orbit for decades.