c) Microbial Mats

The unique color of Yellowstone National Park’s Grand Prismatic Spring is caused by microbial mats. These mats are composed of bacteria and other microbes that thrive in the hot and mineral-rich waters of the spring. The colors in the microbial mats vary from green to red, depending on the ratio of chlorophyll to carotenoids and the temperature of the water, which affects the types of bacteria present. The Grand Prismatic Spring, the largest hot spring in the United States, is renowned for its striking coloration and its vast size, making it one of the most photographed features in Yellowstone.