One of our favorite spots in the entire park! This Spring is truly mesmerizing and seeing it from above is (in our opinion) much better than walking next to it. It is the largest hot spring in the United States, and the third largest in the world! The vibrant colors of Grand Prismatic Spring are primarily due to thermophile bacteria that thrive in the different temperature gradients of the hot spring water. These bacteria produce pigments, including chlorophyll and carotenoids, which give them their characteristic colors, ranging from green to red. The central part of the spring is sterile due to the extreme heat, resulting in its blue color.