Rainbow Pool

Overview

Rainbow Pool is a classic Yellowstone hot spring on the Black Sand Basin boardwalk, just north of Old Faithful. It’s a constantly overflowing pool (not a geyser), so you’ll usually see a calm, steaming surface rather than eruptions. The short boardwalk loop makes it an easy, rewarding stop between bigger headliners.

What You’ll See

Expect a deep blue center framed by vivid rings of yellow, orange, and rust. Those colors come from thermophiles—heat-loving microbes and cyanobacteria—forming dense mats that change with temperature bands around the pool. Their pigments (including carotenoids) both harvest light and protect from intense sun, which is why the hues can shift a bit with season and temperature.

Geology in Brief

Hot springs like Rainbow Pool have open plumbing that lets superheated water circulate and overflow continuously. Geysers, by contrast, need a constriction to build pressure and erupt intermittently. Here, convection keeps the pool replenished and the colors fresh along its rim.

Safety and Etiquette

Stay on the boardwalk—ground in thermal areas is thin and unpredictable, and the water can be near boiling. Don’t touch the water or toss coins/objects; even small disturbances can sterilize the fragile microbial mats and scar the colors. Bison, elk, and birds wander these basins—give them space and turn back rather than stepping off the walkway.

Logistics

This is a boardwalk stop, not a serviced facility. There are no restrooms or picnic tables at the feature, and food isn’t allowed on the boardwalks. Use facilities in nearby developed areas like Old Faithful.

Best Time to Visit

Colors typically pop in mid-morning to midday when the sun is higher and steam tends to lift. On cold mornings, steam can blanket the pool and photography gets tricky. In peak season, arrive early or later in the day for easier parking and thinner crowds.