The largest hot spring in the US. A rainbow of heat-loving bacteria. Do not touch the water.
Grand Prismatic is 90 metres wide — the largest hot spring in the United States and third-largest on earth. Its extraordinary color rings are produced by different species of thermophilic (heat-loving) bacteria living at different temperatures from the scalding blue center (90°C, too hot for life) outward through yellow, orange, and brown rings where progressively lower temperatures support successive microbial communities. The deep blue center contains no life at all — only the color of pure water in depth.
- 2,224 m
Pools & saunas
Waters & pools
- Hot spring
- 1 pools
- 70–100°C
- Open-air
Gallery
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Worth knowing
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Color rings produced by heat-tolerant bacteria living at different temperatures
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Center temperature 87°C — too hot for any life
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Third-largest hot spring on earth at 90 metres diameter
An insider's tip
For the aerial view that appears in every photograph, hike the short Fairy Falls trail to the overlook. The boardwalk at the spring itself gives no sense of its full scale.
Don't leave without
Take the Fairy Falls trail to the overlook at sunset for the full prismatic color display. Early morning in summer gives the best steam for drama.
In brief
- Location
- Midway Geyser Basin, Yellowstone, United States
- Type
- Natural Monument
- Temperature
- 87°C avg
- Access
- Walk-in
- Elevation
- 2,224 m
- Entry
- Paid / ticketed
- Soakable
- Visual only — do not enter
In the water
Best season
May – September for color vibrancy; any season for steam
On the map
44.5250°N · 110.8381°W
