Emerald Pool Hot Springs, Yellowstone

The bright colors found in Yellowstone's hot springs come from thermophiles—microorganisms that thrive in hot temperatures. So many thermophiles are grouped together—trillions!—that they appear as masses of color and can form algae-like mats.

Different types of thermophiles live at different temperatures within a hot spring and cannot tolerate much cooler or warmer conditions. Yellowstone's hot water systems often show different color gradations of living, vibrant colors where the temperature limit of one group of microbes is reached, only to be replaced by a different set of thermophiles.

Two common bacteria, Phormidium and Oscillatoria, contribute to the orange color.
Carotenoids: The orange hue comes from carotenoid pigments produced by these bacteria. Carotenoids serve as a natural sunscreen, shielding the microbes from the intense sunlight in Yellowstone’s summer.
5N4A3771