Grand Prismatic Spring in Yellowstone N.P. is the third largest hot spring on earth ( with water temperature of 160 ºC ) but considered the most fascinating one.
Algae and pigmented bacteria in the microbial mats that grow around the edges of the mineral-rich water spring change color dependent on the ratio of chlorophyll to carotenes produced by these organisms.
( image courtesy of www.nationalgeographic.com )
This is definitely one of the sights you want to see in your lifetime.
Date: August 23rd, 2010.