Black Pool 1
Black Pool is part of the West Thumb Geyser Basin of Yellowstone National Park, Wyoming. The brilliant colors that hot springs are typically known for are caused by microorganisms that live in communities of thick bacteria mats in the thermal waters of the hot spring. Black Pool was originally named for deep black looking water that was caused by dark brown bacteria living in the thermal water. In 1991, the water temperature rose and the color of the bacteria changed to the brilliant red, orange and yellow colors that can be seen today. The deep blue colors are caused by high concentrations of minerals in the water that bubbles up from deep within the earth crust.