Grand Prismatic Spring is one of the largest and most beautiful examples of a common hydrothermal feature in Yellowstone, hot springs. The prismatic or colorful features come from several sources; the deep blue in the center is the clear super-heated water circulating up from the subterranean heat source under the Park. As the water cools at the surface, some of it sinks back down, and some of it runs off in shallow rivulets in all directions of the compass. As the water cools at the edges of the pool and on the sinter terraces, bacteria and algae live and prosper producing a rainbow of colors. From this aerial perspective, a pair of convection currents, like a pair of eyes, is visible where the water boils up from the immense heat source below. This hot spring was specifically mentioned in Osborne Russell’s Journal of a Trapper , by the name of Boiling Lake, which apparently was a name given to it by Rocky Mountain fur trappers in the 1830s.