Not long ago, Black Pool really was black. Lower water temperature allowed thick mats of dark green and brown thermophiles to grow in the pool, causing it to appear black. The water temperature rose during the summer of 1991, killing these organisms. Black Pool also erupted that summer and several times the following winter. Like Abyss, Black Pool is now one of Yellowstone's most beautiful pools.
Survey Date: June 22, 2000
Geographic Area: West Thumb
Thermal Region: West Thumb Geyser Basin
Thermal Complex: Lower Group
Ranger District Contact: Grant District, Matt Vandzura (307) 344-2601
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