Midway Geyser Basin is a small area with big appeal. It houses the Giant Prismatic Spring which is the largest thermal spring at Yellowstone and the largest feature at the Midway Geyser Basin. It measures roughly 350 by 250 feet and its temperature runs between 150 and 180 degrees.
The Spring is known for brilliant bands of bright red, green and yellow rings around a deep blue bullseye. The various colored rings are due to different types of bacteria thriving at different temperature bands that form as the water deepens in the pool. Colors vary somewhat by season. The rings tend to be orange and red in summer and lean more toward dark green in the cooler winter months At its deepest point Giant Prismatic Spring is about 120 feet deep. More than 500 gallons of hot water run out of the spring every minute to help fuel the Firehole River.
This is a good stop to combine with your trip to Firehole Falls for some swimming! This is another in our series on Top 10 Activities for families on vacation with teens and tweens at Yellowstone.