West Thumb Geyser Basin, Yellowstone National Park. According to their website: emperature 172°F Dimensions 30x57 feet. Depth 53 feet. Abyss Pool is a colorful and interesting pool in the West Thumb Geyser Basin. Abyss is the deepest pool known in Yellowstone and received its name for its abyss-like depth. The dark green-colored water gives the illusion of a bottomless pool. Vandalism may have changed this pool's temperature. Coins and other debris thrown in have caused the vent to plug. The reduced spring flow also reduced the pool temperature, allowing abundant algae growth along the edge and run-off channels. The extensive microbial mats now support ephydrid flies, spiders and killdeers. An unusual eruption in 1987 caused the pool to surge and temporarily destroyed the microbial mats.
