In Colombia, Rio Cano Castales, or the ‘river of five colors’, is a special place where for a brief period of time every year when the conditions are just right, the river explodes with vibrant colours your eyes won’t believe. During the short span between the wet and dry season, 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 countless shades in between.
The river can be found in the Serrania de la Macarena in the province of ****. It runs to the east, flowing into the Guayabero river. It is approximately 100km long and no more than 20 meters wide. The phenomenon can be observed during for a special period of a few weeks from June through to November when the temperature is just right. Traveling to the river is not easy as you must fly to the small town of La Macarena and trek through unmarked trails into the national park from there.
http://atlasobscura.com/place/cano-cristales http://en.wikipedia.org/wiki/Ca%C3%B1o_Cristales 
