Rainbow Pool is a large, 100-foot (30.5-m) diameter pool that has a few sporadic eruptions in the history of the park, the last being in 1996. The pool overflows its sinter rim and runoff travels down the sinter shelf and eventually reaches the Firehole River. The clear blue pool is surrounded by orange thermophiles at the pool rim, and those thermophiles continue growing into the outwash channels.

Rainbow Pool has an average temperate of 149.3°F (65.2°C), an average pH of 3.5, and an average conductivity of 2306 uS/cm.

Hot Springs

Hot springs are the most common hydrothermal features in Yellowstone. Their plumbing has no constrictions.

Superheated water cools as it reaches the surface, sinks, and is replaced by hotter water from below.

This circulation prevents water from reaching the temperature needed to set off an eruption.

Use Caution in Hydrothermal Areas

• Stay on boardwalks and designated trails.
• Hydrothermal water can severely burn you.
• Never run, push, or shove.
• Supervise children at all times.
• Do not scratch hydrothermal mats.

You are responsible for your safety.

Think safety, act safely. Yellowstone is a dangerous place.