Emerald Pool is sometimes a lovely shade of green. That makes sense when you consider the water is a deep blue and the lining of the pool is a bacteria-laden yellow. However the pool has been decreasing in temperature because of a combination of natural debris and materials thrown into the pool by visitors. This is causing the rim of the pool to darken to a brown color.

I photographed this pool with and without a polarizing filter. Usually I preferred the photographs of the hot springs and geysers with the polarizer to cut the reflections from the surrounding features and sky. Not so this time. When I used the filter, the reflection of the sky and trees disappeared and the pool was partly a dark brown and partly a lighter muddy color. I preferred the photographs of Emerald Spring with the added colors from the reflections.

This hot spring is part of the Black Sand Basin located near the Old Faithful Complex in Yellowstone National Park.