The Grand Prismatic Spring, Yellowstone, is the largest hot spring in the U.S., third largest in the world, about 370 feet (112.8 m) in diameter and over 120 feet (37 m) deep. The colors come from bacteria that grow near the edges; the center is sterile. The spring discharges 560 US gallons (2,100 L) of water at 160 °F (70 °C) every minute. Photo taken August 18th. Click for larger version.
