Yellowstone's biggest hot spring is rainbow-coloured because of heat-loving microbes

Grand Prismatic Spring, the largest hot spring in the United States, gets its rings of orange, yellow and green from mats of thermophilic bacteria and archaea living at different temperatures around its rim. The scalding blue centre is too hot for almost anything to survive, so it just reflects sunlight instead. Some of these microbes tolerate heat that would kill most other life on Earth.

— U.S. National Park Service, Grand Prismatic Spring — Yellowstone National Park geothermal resources