Opal Pool is a hot spring in the Midway Geyser Basin of Yellowstone National Park, Wyoming.

[1] Though usually active as a hot spring, Opal Pool is considered a fountain-type geyser.

Eruptions occur suddenly following visible convection in the pool, but are unpredictable.

Much smaller splashes seconds apart stretch the total duration to about 1 minute.

In 2005 Opal completely drained, but refilled as a vivid green pool in 2008.