NASA Images Show Decreased Clarity in Lake Tahoe Water

Images from the Advanced Spaceborne Thermal Emission and Reflection Radiometer aboard NASA's Terra satellite, launched in 1999, illustrate the state of gradually decreasing water clarity at Lake Tahoe, one of the clearest lakes in the world. The images are available at: http://asterweb.jpl.nasa.gov/default.htm. In the image on the left, acquired in November 2000, vegetation can be seen in red. The image on the right, acquired at the same time by a different spectral band of the instrument, is color-coded to show the bottom of the lake around the shoreline. Where the data are black, the bottom cannot be seen. Scientists monitoring the lake's water clarity from boat measurements obtained since 1965 have discovered that the lake along the California-Nevada border has lost more than one foot of visibility each year, according to the Lake Tahoe Watershed Assessment, a review of scientific information about the lake undertaken at the request of President Clinton and published in February 2000. The most likely causes are increases in algal growth, sediment washed in from surrounding areas and urban growth and development. http://photojournal.jpl.nasa.gov/catalog/PIA03854