Grand Prismatic Spring, Yellowstone National Park, Wyoming. First described by European explorers in 1839 as a "boiling lake" and later named for its resemblance to the colors of white light being separated by passing through a prism. These colors are microbial mats, thriving in the mineral-rich water. The color depends on the ratio of chlorophyll to carotenoids, and reflects the temperature gradient in the water as it cools down the farther it is from the spring. The center of the spring (the blue) is sterile due to the extreme heat. This spring is 370 feet in diameter, 160 feet deep, produces 560 gallons per minute, and is the 3rd largest spring in the world.