The centre
A deep natural blue.
John Manard — CC BY-SA 2.0 · Pedro Szekely from Los Angeles, USA — CC BY-SA 2.0 · zoxcleb — CC BY-SA 2.0 · Yellowstone National Park — Public domain · Yellowstone National Park — Public domain
Grand Prismatic Spring is the largest hot spring in Yellowstone National Park and the third largest in the world, after Frying Pan Lake in New Zealand and Boiling Lake in Dominica. It lies in the Midway Geyser Basin and is known for colours matching most of the rainbow, one of America's best known natural pictures. Fur trappers noted a «boiling lake» here in 1839, about 90 m across, and the Washburn Expedition passed by in 1870. Geologists of the Hayden Survey named it in 1871 for its striking colours of red, orange, yellow, green and blue. The colours come from mats of heat-loving microbes around the edges, and change with the season, orange and red in summer and dark green in winter. The deep blue in the centre is simply the natural colour of water. Thick steam rises from the surface, and orange streaks spread like sun rays over pale ground, among old dead tree trunks. It is 7 km in a straight line from Old Faithful. A boardwalk runs beside it, but the finest view is from a raised overlook on the Fairy Falls trail, where you see the colours from above. Choose a warm sunny day after mid morning, when there is less steam. Never leave the boardwalks, as the water is scalding, and bring a hat and water.
A deep natural blue.
Orange and red in summer.
The colours from above.
Midway Geyser Basin, Yellowstone National Park, Wyoming
From the raised overlook on the Fairy Falls trail, not just the boardwalk.
Mats of heat-loving microbes, and the blue is the colour of water.