The Grand Prismatic Spring is the largest hot spring in the US and the third largest in the world. The vivid colors in the spring are the result of pigmented bacteria in the microbial mats that grow around the edges of the mineral-rich water. The bacteria produce colors ranging from green to red; the amount of color in the microbial mats depends on the ratio of chlorophyll to carotenoids and on the temperature of the water which favors one bacterium over another. In the summer, the mats tend to be orange and red, whereas in the winter the mats are usually dark green. The center of the pool is sterile due to extreme heat.

It is impossible to capture the scale of the Spring from ground level. If you look at this photo closely, you will see the boardwalk running through Midway Geyser Basin and ground-level photos typcially capture the fringes of the Spring as well as the steam tinted the color of the bacteria below (which makes for a different and still cool shot.) To get a shot like this requires elevation, either from the top of one of the nearby ridges or from an aircraft.

How I made this image - just south of the Midway Geyser Basin (about a 5 minute drive) is the Fairy Falls trail. It's about a mile walk to the ridge that sits behind the Grand Prismatic and a 5-10 minute climb to the top of the ridge. It is definitely worth the effort and the view is mostly unobstructed with just a few dead lodgepoles around. If you keep hiking the trail, Fairy Falls is another 1.9 miles (.3 miles to the junction) and Imperial Geyser is another 3 miles through the brush. I was hiking solo and did not have bear spray (not recommended!) You can cover six miles pretty quickly when spooked, which I was after I scared something large off the trail to Imperial Geyser.