Rainbow Pool

Rainbow Pool, one of the most visually stunning thermal features in Yellowstone National Park, lies between the renowned Morning Glory Pool and Grotto Geyser in the Upper Geyser Basin. True to its name, this spectacular hot spring is a vibrant display of color, with hues ranging from deep blue to green, yellow, orange, and red—creating a dazzling, rainbow-like effect across its surface. 

The pool’s coloration is the result of both its extreme heat and the thermophilic microorganisms that thrive in its mineral-rich waters. These heat-loving microbes form colorful mats along the edges, with each hue corresponding to a particular species that can survive at different temperature ranges. The vivid contrast between the crystal-clear central waters and the richly colored periphery makes Rainbow Pool one of Yellowstone’s most photographed hot springs.

Rainbow Pool

Quick Reference: Rainbow Pool

Feature	Details
Name	Rainbow Pool
Location	Upper Geyser Basin, Yellowstone National Park, Wyoming, USA
Type	Hot Spring
Diameter	Approximately 100 feet (30.5 meters)
Depth	Unknown (very deep central pool)
Temperature	Average 149.3°F (65.2°C)
pH Level	3.5 (mildly acidic)
Conductivity	2306 µS/cm
Last Known Eruption	1996 (sporadic eruptions have occurred in history)
Coloration	Deep blue center surrounded by orange and yellow thermophiles forming a “rainbow” effect
Water Overflow	Overflows sinter rim and runoff reaches Firehole River
Special Note	Occasionally showed geyser-like activity after the 1959 Hebgen Lake earthquake but now remains calm
Best Viewing Time	Midday for vivid colors under direct sunlight
Accessibility	Easily accessible via boardwalk in the Upper Geyser Basin

Rainbow Pool is a large, 100-foot (30.5-meter) diameter pool that has experienced a few sporadic eruptions in the park’s history, the last one recorded in 1996. These eruptions, sometimes reaching several feet high, added to the intrigue surrounding this magnificent spring. Over time, the pool returned to its tranquil state, resuming its role as a gently steaming, color-rich wonder.

Rainbow Pool has an average temperature of 149.3°F (65.2°C), an average pH of 3.5, and an average conductivity of 2306 uS/cm. Its mildly acidic nature contributes to the unique chemical composition of the surrounding sinter formations. 

The pool overflows its sinter rim, and the runoff travels down the sinter shelf before eventually reaching the Firehole River. The clear blue water at the center transitions beautifully into orange thermophiles around the rim, which continue to spread into the outwash channels, forming striking patterns of color and texture.