The Morning Glory hot spring in the Upper Geyser Basin of Yellowstone National Park in Wyoming, in western United States, is a sight to behold for tourists.
Its distinctive colours are due to bacteria that survive in the hot water, although its vivid hue has changed from its original blue to yellow and green after an accumulation of debris thrown in by tourists.
About three million tourists flock to the park, compared with the one million in the 1940s, which has led to the build-up of debris.
In 1950, the water level was lowered by siphoning that induced the pool to erupt. Socks, bath towels, handkerchiefs and about $130 in coins came up.
Unless some subterranean shift happens and more hot water flows to the surface, Morning Glory will never be fully blue again.