Giant Prismatic Spring is the largest hot spring in the United States and the third largest in the world. No drive around Yellowstone National Park is complete without a stop to see the beautiful colors of this spring yourself in Midway Geyser Basin. The spring itself is around 110 meters in diameter and over 50 meters deep. Over 2,000 liters of 160-degree water is discharged from the spring per minute. This causes a constant rushing stream of water that tumbles into the Firehole River.
The nature walk around Midway Geyser Basin lets you see Excelsior Geyser Crater, Turquoise Pool, and Opal Pool in addition to the Grand Prismatic Spring. Due to the low angle of visibility from the boardwalk and the constant steam, these other thermal features can be even more visible and impressive in person than Grand Prismatic Spring and are not to be missed.
The extremely vivid colors of the spring are caused by microbial mats around the edge of the mineral-rich water. These mats change in color throughout the year, ranging from green in the winter to orange and red in the summer. Be careful on the boardwalks around the spring as there have been injuries and even deaths when visitors fall in, sometimes due to the temptation to retrieve a lost hat due to the strong winds.