Microorganisms play a large part in coloring hot springs at Yellowstone National Park. According to the National Park Service, "The color of Emerald Spring comes from the inherent blue of the water combined with the yellow of the sulfur-coated pool. The water in this 27-foot deep pool is so hot (close to boiling) that only the most heat-tolerant thermophiles can survive. In sulfur-rich hot springs, such as Emerald Spring, some microorganisms use sulfur as their energy source. Byproducts from these reactions can be used by other microbes. This kind of “recycling” ties the various microorganisms into diverse functioning communities."