Black Pool

Black Pool, located in the West Thumb Geyser Basin of Yellowstone National Park, is one of the most visually captivating and scientifically fascinating thermal features in the park. Despite its ominous name, Black Pool is not black at all today; instead, it glows with deep shades of blue and turquoise that reflect both its immense depth and the purity of its hot, clear water. 

The name “Black Pool” originated from the early 20th century when the pool’s appearance was dramatically different. At that time, cooler water temperatures allowed thick mats of dark green and brown thermophiles—heat-loving microorganisms—to thrive on the pool’s surface and edges. These microorganisms gave the pool its dark, almost black coloration. However, a shift in geothermal activity during the 1990s dramatically increased the water temperature, killing off most of the thermophiles and revealing the brilliant blue depths that visitors see today.

Black Pool

Black Pool

Quick Reference: Black Pool

Feature	Details
Name	Black Pool
Location	West Thumb Geyser Basin, Yellowstone National Park, Wyoming, USA
Type	Hot Spring
Water Temperature	Approximately 180°F (82°C)
Depth	About 25 feet (7.5 meters)
Color	Deep blue to turquoise (formerly black due to thermophiles)
Geological Context	Lies within the West Thumb Caldera, formed by an eruption ~150,000 years ago
Unique Facts	Once appeared black when cooler; turned blue after temperature rose, killing thermophiles
Notable Activity	Experienced brief eruptive behavior during a hydrothermal disturbance in the 1990s
Accessibility	Easily viewed from the West Thumb Geyser Basin boardwalk
Safety Note	Stay on boardwalks; the water is extremely hot and can cause severe burns

Today, Black Pool stands as one of the most striking examples of Yellowstone’s geothermal beauty. Measuring about 30 feet (9 meters) across and descending to an estimated depth of over 25 feet (7.5 meters), it presents a mesmerizing gradient of blues, from deep sapphire at the center to lighter aquamarine near the rim. The water temperature generally hovers around 180°F (82°C), hot enough to prevent the growth of most microorganisms, which keeps the water exceptionally clear. Visitors standing along the boardwalk can often see bubbling along the edges of the pool and rising columns of steam that shimmer in the cool mountain air.

Black Pool’s location near the shore of Yellowstone Lake adds to its picturesque appeal. The contrast between the lake’s cold, tranquil waters and the pool’s steaming surface creates one of the park’s most photogenic scenes, especially in the early morning when fog drifts through the basin. The entire West Thumb Geyser Basin, where Black Pool is found, sits within a small volcanic crater formed during a massive eruption roughly 150,000 years ago. This caldera setting fuels the hydrothermal features that make the area so unique.

For visitors, Black Pool offers an unforgettable experience of nature’s artistry and volatility. It’s easily accessible along the West Thumb Geyser Basin boardwalk, allowing close but safe viewing. Standing before the vivid waters, one can’t help but feel awe at the living, breathing geothermal world beneath Yellowstone’s surface. Black Pool is more than a beautiful hot spring—it’s a living reminder of change, adaptation, and the power of nature’s inner heat that continues to shape the landscape of Yellowstone.