Living Bacteria Paint This Wyoming Hot Spring in Brilliant Blues, Oranges, and Yellows

Grand Prismatic Hot Spring, Wyoming

Grand Prismatic can cook you in minutes.

But for certain bacteria, it’s paradise. These tiny organisms create the rainbow bands that make America’s largest hot spring look like a giant eye staring up from the earth.

Here’s how microscopic life creates one of nature’s most stunning displays.

Grand Prismatic Hot Spring

Grand Prismatic is America’s biggest hot spring and the world’s third largest, behind only Frying Pan Lake and Boiling Lake in Dominica.

It sits in Yellowstone’s Midway Geyser Basin, stretching 370 feet across—bigger than a football field—and plunging deeper than a 10-story building.

Every minute, 560 gallons of steaming water pour into the nearby Firehole River, keeping those famous rainbow colors bright.

Discovering the Spring

Fur trappers first wrote about the spring in 1839, describing a huge “boiling lake” 300 feet wide. The Washburn expedition visited in 1870 and noticed both the colorful pool and a 50-foot geyser nearby they named Excelsior.

Before that, however, Native peoples have already known about these hot springs thousands of years before their “discovery”.

The Shoshone, Crow, and Blackfeet tribes have long used these springs for cooking and medicine.

How It Got Named

Ferdinand Hayden named the spring in 1871 while leading the first government-funded study of Yellowstone. Congress gave his team $40,000 to map the area, and their work made Yellowstone America’s first national park a year later.

They called it “Grand Prismatic” because its color bands—red, orange, yellow, green, and blue—match what happens when light passes through a prism.

A Volcanic Heat

The spring exists because of Yellowstone’s underground supervolcano. This giant magma chamber heats rainwater that seeps down through cracks in the earth.

Once hot, this water becomes lighter and rises back up. Unlike geysers that build pressure and explode, hot springs have open channels for steady flow.

This creates a simple cycle: hot water rises, cools at the surface, sinks down, and fresh hot water takes its place.

Too Hot for Life in the Middle

The center of Grand Prismatic reaches 188°F, which is hot enough to cause instant third-degree burns. Nothing can live in this scorching middle.

As water flows outward, it cools bit by bit. Each temperature drop creates zones where different heat-loving bacteria can survive.

Why the Center Looks Blue

The bright blue center isn’t from chemicals or bacteria, it’s just what deep, clean water looks like. When sunlight hits pure water, blue wavelengths bounce back while other colors get absorbed.

The extreme heat keeps this center sterile and crystal clear. No living thing survives there to cloud the water.

The spring’s 121-foot depth makes this blue even more intense as more water filters more light.

Tough Bacteria Make the Yellow Ring

Moving from the blue center, you’ll see a bright yellow band formed by bacteria called Synechococcus. These tiny organisms somehow thrive in 165°F water that would kill most living things.

These heat-lovers have special proteins that don’t break down in temperatures that would destroy normal cells.

To handle harsh sunlight, they make pigments that work like sunscreen. Under normal conditions, they’d look green, but extreme heat forces them to produce yellow protection.

Orange and Red Rings at the Edges

As water cools to about 149°F, different bacteria create the orange section. At the “cool” 131°F outer edge, you’ll find deep red-brown colors.

Bacteria from the Deinococcus-Thermus family form bright orange streamers that flow with the current. The outer rings hold the most diverse bacterial mix, creating the richest colors.

These bacteria stack in layers based on their temperature needs, forming a living mat around the Grand Prismatic.

The Colors Change with Seasons

During summer’s intense sunlight, bacteria produce more orange and red protective pigments, making colors pop when most tourists visit.

Winter brings gentler sun and slightly cooler temperatures, so bacteria make more chlorophyll for better light absorption. This shifts the colors toward darker green.

The Boat That Explored the Boiling Center

Park Geologist Rick Hutchinson built a custom boat in the 1990s called “Little Dipper” to study the dangerous center. This eight-foot craft had flotation chambers to prevent sinking and a center porthole for safe measurements.

His team ventured into the boiling middle where they recorded temperatures, tested water chemistry, and measured the depth at over 120 feet.

Hutchinson continued this work until his death in a 1997 avalanche.

How These Bacteria Changed Medicine

Bacteria from these hot springs revolutionized science. In 1966, microbiologist Thomas Brock discovered Thermus aquaticus living in nearly boiling water, something scientists thought impossible.

This tough bacterium makes a heat-resistant enzyme that became the foundation for PCR, a technique that copies DNA. This discovery earned a Nobel Prize.

PCR now powers DNA forensics, genetic testing, human genome research, and COVID-19 tests, all thanks to hot spring bacteria.

Visiting Grand Prismatic Spring

You’ll find Grand Prismatic Spring at Midway Geyser Basin, Grand Loop Road, Yellowstone National Park, WY 82190.

Yellowstone charges $35 for vehicles (valid 7 days) and is open 24/7 year-round. Park at the small Midway Geyser Basin lot or roadside turnouts.

You can access the spring via an easy 0.8-mile boardwalk walk. For overhead views, hike 1.2 miles from Fairy Falls parking lot to Grand Prismatic Overlook.

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