Temperature 132°F Dimensions 40x75 feet. Depth 30 feet. Black Pool is one of the largest springs in the West Thumb Geyser Basin. The dark-colored water is the combination of the natural, transparent blue of the water and the orange algae lining of the pool. The low temperature of the pool is responsible for the abundant growth of the orange-colored microbial mats. Algae and cyanobacteria in combination with sinter deposits have created coral-like formations on the sides of the pool but these are visible for only a few feet. The pH of Black Pool is a slightly alkaline 7.8.
