Midway Geyser Basin and Grand Prismatic Spring: The Largest Hot Spring in USA

In Yellowstone National Park, you’ll find a breathtaking and radiant natural marvel: the Grand Prismatic Spring. This is the biggest hot spring in the United States and it’s ranked third globally. Visitors are continually charmed by its alluring hues and exceptional characteristics, making it a must-visit attraction.

Geological history

The spring is a testament to the geological forces that have shaped the landscape of Yellowstone National Park over millions of years.

The park sits atop a volcanic hotspot, which has resulted in a wealth of geothermal features, including geysers, hot springs, and mud pots. The formation and development of the spring are closely tied to the area’s unique geology.

Yellowstone National Park Grand Prismatic Spring Details
Jason Carter / Sharetheexperience

Around 2.1 million years ago, the Yellowstone Caldera was formed during a massive volcanic eruption. The heat from the underlying magma chamber continues to shape the park’s landscape to this day.

The spring, along with other geothermal features in the park, owes its existence to this geothermal activity.

The spring is situated within the Midway Geyser Basin, which is home to several other notable hot springs and geysers. Hot water from deep within the Earth’s crust rises to the surface through a network of fissures and cracks, dissolving minerals from the rocks along the way.

The dissolved minerals, primarily silica, are then deposited around the edges of the spring, forming the iconic, colorful microbial mats and sinter terraces seen today.

What to see at Midway Geyser Basin?

The Midway Geyser Basin is home to several geothermal features, including geysers, hot springs, and fumaroles.

Other notable geothermal features in the Midway Geyser Basin include Excelsior Geyser Crater (the largest active geyser crater in the world), Opal Pool (a small hot spring), Turquoise Pool (a big hot spring).

Yellowstone National Park Grand Prismatic Spring Map
Yellowstone National Park - Midway Geyser Basin & Grand Prismatic Spring map

Excelsior Geyser

The Excelsior Geyser is an impressive sight to behold within the Midway Geyser Basin. This is the first geyser you come across on your trip here as you make your way along the wooden platforms. Excelsior Geyser is one of two large geysers in the Midway Geyser Basin in Yellowstone National Park.

Yellowstone National Park Grand Prismatic Spring Excelsior Geyser
Excelsior Geyser eruption & crater sixthland / Flickr

Once one of the world’s largest geysers, it has now transitioned into a hot spring, discharging more than 4,000 gallons (15,142 liters) of boiling water per minute into the Firehole River.

The pool measures approximately 200 feet by 300 feet (61 meters by 91 meters) and reaches depths of over 80 feet (24 meters). The striking blue color of the water and the steam rising from its surface create a captivating scene that visitors should not miss.

Grand Prismatic Spring

The spring is the largest hot spring in the United States, and is located in Yellowstone National Park.

The spring gets its name from the great amount of heat that causes water to evaporate and form a prism. The spring is about 360 feet across and is surrounded by a boardwalk so that visitors can get a close up view.

Yellowstone National Park Grand Prismatic Spring Close Up
Andrew Parlette
Yellowstone National Park Grand Prismatic Spring Air Look
Eric Henderson

The intense heat of the spring creates an amazing effect on the surrounding area. The water evaporates so quickly that it forms a cloud of steam that can be seen for miles.

The bright colors are created by bacteria that thrive in the hot water. The different colors indicate different temperatures, with the blue being the coolest and the yellow being the hottest.

Why is the Grand Prismatic Spring so colorful?

The spring’s captivating colors are a result of various factors, including the presence of heat-loving microorganisms, water temperature, and the mineral content of the spring. Let’s explore these factors in more detail:

Microorganisms: At the heart of the spring’s color spectrum lies an assortment of heat-loving microorganisms known as thermophiles. These microscopic life forms thrive in the extreme temperatures of the hot spring and form dense mats of pigmented bacteria.

The different colors seen in the spring are due to the varying types of thermophiles and the pigments they produce. For instance, cyanobacteria create shades of green and blue, while other thermophiles generate hues of orange, yellow, and red.

Water Temperature: The temperature of the water plays a significant role in determining the colors. The center of the spring, where water temperatures can reach up to 189°F (87°C), is a deep, vibrant blue.

This blue hue is due to the absorption and scattering of light by the water, which allows only blue wavelengths to be reflected back to our eyes.

As the water flows outward and cools, it creates an environment suitable for various thermophiles, which in turn produce the stunning colors seen around the edges of the spring.

Mineral Content: The water is rich in minerals that have dissolved from the surrounding rocks. These minerals, including silica, iron, and manganese, contribute to the vivid colors displayed by the spring.

For example, the orange and red hues often seen at the edges of the spring are the result of iron oxides in the water.

In summary, the breathtaking colors are a fascinating interplay between the unique biology of thermophiles, the varying water temperatures, and the rich mineral content of the spring.

This complex interrelationship creates an awe-inspiring natural wonder that continues to captivate visitors and scientists alike.

What makes the Grand Prismatic Spring so special?

The spring is nothing short of a mesmerizing natural masterpiece, its ethereal beauty capturing the hearts and imaginations of all who behold it.

As the crown jewel of Yellowstone National Park, this extraordinary spectacle proudly claims the title of the largest hot spring in the United States.

Its enchanting allure is magnified by the tapestry of colors that dance across its surface, weaving an intricate story of geological wonder.

The spring’s majesty is further accentuated by the fact that it stands among the world’s most captivating geothermal features, sharing the limelight with the likes of New Zealand’s Frying Pan Lake and Dominica’s Boiling Lake.

How can I get the best view of Grand Prismatic Spring?

For the best view of the spring, consider hiking the 0.8-mile (1.3 km) one-way trail to the Grand Prismatic Spring Overlook.

The trailhead is located at the Fairy Falls Trail parking area, approximately 1 mile (1.6 km) south of the Midway Geyser Basin parking area. This short hike offers an elevated perspective, allowing you to fully appreciate the spring’s vibrant colors and size.

Yellowstone National Park Grand Prismatic Spring Overlook
After a short trail to the overlook, you will see this wonderful pool from the viewing platform. Rebecca Latson / Flickr

Visiting the overlook allows you to take photos of the boiling lake from different angles. You can see a panoramic view of the geyser. It is not a difficult road, it can be walked easily.

When you pass the viewing platform 0.3 miles, turn left and continue 1.30 miles, you will come across a waterfall called Fairy Falls. It is not a great waterfall, but it is preferable if you are looking for an excuse to walk a bit.

Yellowstone National Park Fairy Falls Aerial View
Fairy Falls trail Google Earth

Opal Pool

Opal Pool is another gem of the Midway Geyser Basin, offering a serene and colorful experience for visitors. Opal Pool is the smallest of them all.

This hot spring features a beautiful blue hue, surrounded by shades of green, yellow, and orange created by the microbial mats living along its edges. Due to its small width, it is the pool that gets covered with ice the fastest, especially in winter, and the one that thaws the longest because it does not have enough steam.

While the pool is usually calm, it occasionally erupts as a geyser, making it an unpredictable and fascinating feature to observe. Like the others, it is important not to get too close to it.

Yellowstone National Park Opal Pool
Opal Pool Tashnuva
Yellowstone National Park Turquoise Pool
Turquoise Pool Anak Tok / Flickr

Turquoise Pool

As the name suggests, Turquoise Pool is known for its stunning turquoise color. This hot spring is surrounded by intricate sinter formations and vibrant microbial mats, creating a visually striking scene.

The Turquoise Pool is shallower and cooler than some of the other hot springs in the basin, allowing for a greater diversity of thermophilic microorganisms and contributing to the vivid colors on display.

Tips for visiting Midway Geyser Basin

As you venture into the realm of awe-inspiring geysers and hot springs, it’s crucial to tread lightly, for these captivating natural wonders can swiftly transform into treacherous snares for the unwary.

  • The alluring beauty of geysers and hot springs belies a lurking peril: their scalding waters. One misstep could plunge you into a boiling cauldron, sealing a harrowing fate. These hypnotic water features not only harbor searing heat but also exude steam that can singe skin and inflict grave burns. The heat permeating the air can also induce dehydration and trigger heatstroke.
  • To safely immerse yourself in the enchanting spectacle, it’s imperative to heed cautionary measures. Traverse the area by following designated trails and boardwalks, resisting the urge to touch or dip into these enticing yet deadly aquatic wonders.
  • The area surrounding the springs teems with a rich tapestry of wildlife as diverse as the spring’s prismatic hues. Elk, bison, deer, pronghorn, and a host of other creatures call this vibrant landscape home. As you explore, treat these majestic beings with respect and maintain a safe distance to avoid disturbing their tranquil existence.

By adhering to these simple yet vital safety guidelines, you can bask in the splendor of this extraordinary place, unencumbered by the specter of danger.

When to visit the Grand Prismatic Spring?

In cold weather, the hot vapor emitted at low temperatures mixes with the cold air to create dense smoke and fog. Therefore, visiting during the warmer months (from May to September) will allow you to see the colors better.

FAQs about Midway Geyser Basin

How hot is the Grand Prismatic Spring?

The spring is incredibly hot, with temperatures in the center of the pool reaching up to 189°F (87°C).

As the water flows outward from the center, the temperature gradually decreases, creating a range of temperatures that support different types of heat-loving microorganisms. This variation in temperature is one of the factors contributing to the vibrant colors seen around the edges of the spring.

Can you swim in the Grand Prismatic Spring?

Swimming is strictly prohibited due to the extreme temperatures and the fragile ecosystem it supports. The National Park Service enforces regulations to protect the spring and its unique features, and violating these rules can result in fines, penalties, or even criminal charges.

Yellowstone National Park Grand Prismatic Spring People
Jason Jeff Hebert / Flickr

What happens if you touch or swim in the Great Prismatic Spring?

Touching or swimming is not only illegal but also extremely dangerous. The scalding water can cause severe burns and even be life-threatening.

Furthermore, human contact with the spring can damage the delicate microbial mats and disrupt the ecosystem, which in turn impacts the spring’s appearance and health. Never step off the boardwalks.

Does the Grand Prismatic Spring smell?

Yes, it smells. It does have a distinct smell, often described as a “rotten egg” odor. This smell is due to the presence of hydrogen sulfide, a gas produced by some of the thermophilic microorganisms living in the hot spring.

While the smell may be strong and unpleasant at times, it is a natural byproduct of the unique ecosystem found within the spring.

Best times to visit for optimal viewing

It is a year-round attraction, but the best time to visit for optimal viewing depends on the weather and the time of day. The spring’s vibrant colors are most visible on sunny days when sunlight can penetrate the steam rising from the hot water.

Therefore, visiting during the summer months from June to September, when the weather is generally clear and warm, will maximize your chances of witnessing the spring’s full spectrum of colors.

Additionally, consider visiting during the morning or late afternoon when the sun is lower in the sky. This will reduce glare on the water’s surface and make the colors more pronounced.

Finally, to avoid crowds and enjoy a more serene experience, consider visiting during the shoulder seasons of May or October, when the park is less crowded but still offers favorable weather conditions.

How to get to Grand Prismatic Spring?

Reaching here in Yellowstone National Park involves a combination of transportation methods and some preparation, but with the right information, the journey becomes a smooth and enjoyable experience.

The first step to visiting this place is reaching Yellowstone National Park itself. The park is accessible by car, with five entrance points: North, Northeast, East, South, and West.

  • Personal Vehicle: The most popular option is to use your own vehicle or rental car. This gives you the most flexibility and freedom to explore the park at your own pace.
  • Guided Tours: Several companies offer guided bus tours that include stops at major attractions, including the Great Prismatic Spring. This option allows you to sit back, relax and learn more about the park from knowledgeable guides.
  • Bicycling: Yellowstone has designated bike paths and some visitors prefer to explore the park by bike. However, keep in mind that bicycles are not allowed on boardwalks or trails, so you will need to lock your bike to a designated rack near the spring and continue on foot.

By car: It can be found within Midway Geyser Basin – a location that visitors may reach by utilizing Grand Loop Road – Yellowstone National Park’s primary roadway.

Those coming from entrance near West should take note to traverse around 20 miles (32km) of this path before finally reaching their destination at Midway Geyser Basin’s car parking area. Meanwhile, guests who begin their journey from South entrance must brave a much longer distance of approximately 45 miles (72km).

Parking and Additional Information

Parking at the Midway Geyser Basin can be limited, especially during peak season. Arriving early in the morning or later in the afternoon can increase your chances of finding a parking spot. If the main parking area is full, additional parking can be found along the Grand Loop Road, but be prepared to walk a bit further.

Remember that the boardwalks and trails around the place can be slippery due to the moist environment. Wear sturdy footwear, stay on designated pathways, and follow all posted safety guidelines to ensure a safe and enjoyable visit.



The Grand Prismatic Spring’s mesmerizing display of color and geologic forces never fails to captivate its visitors. Through gaining an understanding of the scientific explanations and historical context surrounding this natural phenomenon, a deeper appreciation for its magnificence can be attained.

To witness the full spectrum of colors that this hot spring exhibits, timing one’s visit during optimal viewing periods is highly recommended.