That is clear, clear water of a blue & gold hot spring: West Thumb, Yellowstone, originally uploaded by abaesel.
Our first day in Yellowstone NP we drove north from Grand Tetons and stopped for a walk around the West Thumb Geyser Basin that is located along the shorline of Lake Yellowstone. A series of boardwalks and paths wind through geysers, hot springs, fumaroles, and geysers at and in the lake's edge. It was a magical introduction to the geysers of Yellowstone. This one here was steaming but the water was crystal clear magnifying the colors of the beautiful spring.