Another thermal pool along the boardwalk in the Midway Geyser Basin is Opal Pool. . Though usually active as a hot spring, approximate temperature of 132 °F (56 °C), Opal Pool is considered a fountain-type geyser though eruptions are infrequent. The first recorded eruption of Opal Pool was in 1947 and it occurred infrequently until they stopped in 1953. The eruptions reemerged in 1979 erupting without much warning. A fact I found interesting: In 2005 Opal completely drained, but refilled as a vivid blue-green pool in 2008. It is still a beautiful oval shaped pool with beautiful colors.