The Grand Prismatic Spring is a hot spring in Yellowstone National Park. It gets its name from the wide array of colors displayed in the spring. Bacteria causes the formation of colors as the bacteria reacts to changes in the water temperature.
The Grand Prismatic is located next to Excelsior Geyser/Spring. Excelsior used to be the largest geyser in the world until it exploded creating the crater that forms the spring as it exists now.
Both the Grand Prismatic and Excelsior feed the Firehole River that flows nearby.