A unique biological wonder, Caño Cristales has been referred as the "river of seven colors," "the river that ran away from paradise," and "the world's most beautiful river."

During a short span between the wet and dry seasons, when the water level is just right, a unique species of plant that lines the river floor called Macarenia clavigera turns a brilliant red. It is offset by splotches of yellow and green sand, blue water, and a thousand shades in between.

http://en.wikipedia.org/wiki/Ca%C3%B1o_Cristales