Blue Star Spring

Blue Star Spring, one of Yellowstone National Park’s most captivating hydrothermal features, sits quietly beside the main boardwalk near Old Faithful in the Upper Geyser Basin. Though small in size, this spring draws visitors for its extraordinary clarity and brilliant blue color that resembles a perfectly cut gemstone glimmering under the sun. 

Its intense sapphire hue comes from the scattering of light within the deep, hot water — a phenomenon caused by the absorption of longer wavelengths and reflection of shorter, blue ones. Surrounding the pool, delicate white sinter deposits form a clean, chalky rim that highlights the striking contrast of its water, making it one of the most photogenic hot springs in the area.

Blue Star Spring 

Quick Reference: Blue Star Spring

Feature	Details
Name	Blue Star Spring
Location	Upper Geyser Basin, near Old Faithful, Yellowstone National Park
Type	Hot Spring (occasionally eruptive in the past)
Appearance	Deep, clear blue water with white sinter edges and subtle thermophilic color bands
Last Recorded Eruption	2002
Average Temperature	190.7°F (88.2°C)
Average pH	8.9
Average Conductivity	1866 uS/cm
Water Depth & Shape	Deep vent with nearly circular outline
Activity	Constant steaming and bubbling; no current eruptions
Surroundings	Sinter terrace with runoff channels supporting colorful microbial mats
Accessibility	Easily visible from boardwalk between Old Faithful and Castle Geyser
Best Viewing Time	Early morning or late afternoon for vivid color and minimal steam
Notable Fact	Named for its brilliant sapphire-blue color resembling a gemstone

Blue Star Spring has a fascinating relationship with the underground hydrothermal network of the Upper Geyser Basin. It shares the same geothermal energy that fuels Old Faithful and other nearby geysers, though it remains primarily a hot spring rather than an active geyser. While Blue Star Spring has been known to erupt, it has not had a recorded eruption since 2002. The spring’s activity today is limited to constant steaming and subtle bubbling, signaling the intense heat and pressure beneath the surface.

The pool maintains an average temperature of 190.7°F (88.2°C), an average pH of 8.9, and an average conductivity of 1866 uS/cm. These factors indicate a high level of alkalinity and mineral content, typical of Yellowstone’s siliceous sinter hot springs. The water flows gently from the spring’s vent, cooling slightly as it trickles across the surrounding terraces, where it supports thin layers of thermophilic bacteria that create subtle bands of yellow, green, and orange color. These microbes thrive in the cooler runoff zones, contributing to the spring’s delicate and colorful beauty.

Visitors can view Blue Star Spring easily from the boardwalk between Old Faithful and Castle Geyser. Its accessibility and location along one of the park’s most popular walking routes make it a frequent stop for photographers and geology enthusiasts alike. The clarity of its water is mesmerizing, revealing details of its vent even several feet below the surface. Early morning visits often provide the most enchanting experience, as steam drifts lightly across the surface while sunlight enhances the pool’s radiant blue tone.