Grand Prismatic Spring

The Grand Prismatic Spring is located within the Midway Geyser Basin in the park. It is the park's hottest spring, at a temperature of 147-188°F, and is the largest spring in Yellowstone._1,2

This spring was discovered in 1839 by European explorers who were members of the American Fur Company. For obvious reasons, they called it the "boiling lake." A second expedition, the Washburn-Langford-Doane Expedition, carefully documented the spring and the area around it.

As noted above, the bacteria can only survive on the outside rim of the spring because the water is too hot for them to live in the middle of the spring. Chlorophyll is what makes the bacteria colored, and different temperatures cause the color to change. The yellow bacteria band lives under harsh conditions and changes colors in the spring and winter-a blue-green color. The orange band represents water that is a little cooler, at around 149 degrees F. The outermost band is 131 degrees F, which is the coolest and is reddish-brown in color, which makes it almost look like lava.₄