The Grand Prismatic Spring: America's largest

America's largest hot spring and third largest in the world, the Grand Prismatic Spring in Yellowstone National Park is about 250 by 300 feet (75 by 91 meters) in size and 160 feet (49 meters) deep, discharging an estimated 560 gallons (2000 liters) of 160°F (71°C) water/minute. The vivid colors in the spring ranging from green to brilliant red and orange are the result of algae and pigmented bacteria in the microbial mats that grow around the edges of the mineral-rich water, the amount of color dependant on the ratio of chlorophyll to carotenoids produced by the organisms. The center of the pool is sterile due to extreme heat. (Photos: Magadelic Rock and Bonnie Sue)