Grand Prismatic Spring in Yellowstone National Park is a beautiful large blue hot spring. Unfortunately on a cold cloudy day like we had the pool is usually obscured by the massive amounts of steam that rise from the surface. On the plus side it made for an interesting backdrop for the runoff streams. Large amounts of water flowing from the spring over sloping ground produce brilliantly colored streams. Thermoacidophilic bacteria that thrive in the hot, acidic waters produce the vivid colors.
(by David Morse)