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Black Pool hot spring, Yellowstone National Park, WY

Black Pool is a hot spring in the West Thumb Geyser Basin of Yellowstone National Park. It was cool enough up until 1991 for dark orange-brown cyanobacteria to grow throughout the pool. When combined with the blue of the water, the pool appeared to be an exceptionally dark green to almost black, hence the name.

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Filename: Black-Pool-Yellowstone-9646.jpg
Copyright: Rozanne Hakala
Image Size: 5616x3744 / 33.9MB; landscape park UNESCO World Heritage Site azure steam WY National Park Service tourism YNP Greater Yellowstone Ecosystem tourist Yellowstone National Park thermophiles mineral deposits West Thumb Geyser Basin USA geothermal bacterial mats Yellowstone algae outdoors Wyoming water bacteria hot spring microorganisms caldera scenic colorful U.S. Yellowstone Plateau thermal Black Pool Rozanne Hakala
Contained in galleries: Yellowstone & Grand Tetons

Black Pool is a hot spring in the West Thumb Geyser Basin of Yellowstone National Park. It was cool enough up until 1991 for dark orange-brown cyanobacteria to grow throughout the pool. When combined with the blue of the water, the pool appeared to be an exceptionally dark green to almost black, hence the name.