I know, I know. It’s not black. That is the name, though, of this very hot pool.
It used to be black. Lower water temperature allowed thick mats of dark green and brown thermophiles (heat-loving microorganisms) to grow in the pool, causing it to appear black. In 1991, the water temperature rose, killing the thermophiles. It also erupted as a geyser that summer and several times the following winter. Black Pool is now a quiet and beautiful pool.
Posted from Old Faithful Inn, Yellowstone National Park