Emerald Pool

Emerald Pool, one of the most enchanting sights in Yellowstone National Park’s Black Sand Basin, captures the essence of nature’s artistry through color, chemistry, and geothermal power. Once celebrated for its stunning emerald-green hue, the pool remains a captivating feature that continues to evolve with time. 

The name “Emerald Pool” was inspired by its brilliant appearance — once a striking blend of deep blue and golden yellow tones that, when combined, created the illusion of a glowing green gemstone. Over the years, however, the pool’s beauty has transformed, mirroring subtle yet fascinating changes in Yellowstone’s hydrothermal dynamics.

Emerald Pool

Quick Reference: Emerald Pool

Category	Details
Name	Emerald Pool
Location	Black Sand Basin, near Upper Geyser Basin, Yellowstone National Park, Wyoming, USA
Feature Type	Hot Spring
Geothermal Classification	Alkaline, non-eruptive thermal pool
Average Temperature	136.3°F (58°C)
pH Level	9 (alkaline)
Average Conductivity	2216 µS/cm
Appearance	Large, steaming pool with orange thermophilic mats and mineral sinter edges
Former Color	Deep blue center surrounded by yellow thermophiles, giving an emerald-green appearance
Current Color	Predominantly orange, amber, and green hues due to temperature drop and thermophile shift
Formation Details	Changes in hydrothermal activity over time have cooled the water and altered microbial life
Surrounding Environment	Thin mineral crust and colorful thermophilic channels in the outwash area
Accessibility	Easily accessible via Black Sand Basin boardwalk; short walk from parking area
Nearby Attractions	Rainbow Pool, Sunset Lake, Cliff Geyser, and Biscuit Basin
Safety Note	Stay on boardwalks; water and ground temperatures are extremely hot and fragile
Fun Fact	Once known for its true emerald color, the pool’s hue changed as water temperatures dropped, altering the microbial composition
Best Viewing Time	Morning or late afternoon for vibrant color contrasts and gentle steam visibility

Located just a short distance from the famous Upper Geyser Basin, Emerald Pool is a large, steaming hot spring framed by delicate mineral deposits and surrounded by vibrant thermophilic life. Thin, solidified sinter forms a fragile crust around the pool’s edge, shimmering in the sunlight and contrasting sharply with the brilliant orange and brown hues that now dominate the water’s outflow channels. These colors are produced by heat-loving microorganisms that thrive in the cooler edges of the spring — an indicator of the pool’s gradual cooling over recent decades.

Emerald Pool was once known for its deep, translucent blue center, which, when combined with a ring of yellow thermophiles, gave the pool its mesmerizing emerald color. However, as temperatures in the pool declined, those yellow organisms were replaced by orange and rust-colored thermophiles, changing its appearance dramatically. Today, the pool exhibits a warmer palette — a blend of deep amber, orange, and greenish tones — revealing how even slight variations in geothermal energy can alter the biological composition of Yellowstone’s hot springs.

The scientific makeup of Emerald Pool is as fascinating as its appearance. With an average temperature of 136.3°F (58°C), an average pH of 9, and an average conductivity of 2216 µS/cm, it exemplifies a moderately alkaline environment that supports a rich diversity of microbial life. The pool’s clear water, though visually inviting, conceals an environment of extreme heat and mineral content that would be deadly to humans and most forms of wildlife. The orange mats lining its bottom and outwash channels are composed of thermophilic bacteria and archaea that thrive in temperatures where few organisms can survive, painting the spring with vivid strokes of natural artistry.

Visitors to Black Sand Basin can easily reach Emerald Pool via the boardwalk trail that winds safely around the area. The pool lies in close proximity to other remarkable features like Sunset Lake and Rainbow Pool, creating one of the most colorful and photogenic landscapes in the park. Standing before Emerald Pool, one can feel both the serenity and volatility of Yellowstone — a reminder that beneath this peaceful beauty lies one of Earth’s most active geothermal systems.

Though its once-vivid emerald hue has faded into warmer shades, Emerald Pool remains one of Yellowstone’s most poetic examples of change. It tells the story of nature’s ability to adapt, evolve, and reinvent its own artistry. For many, it’s not just a hot spring, but a living symbol of the park’s dynamic energy — a gem that continues to shine in new ways, no matter how its colors shift with time.