Deep into the swaths of Colombia's hidden rain forests in the province of Meta near to the Serrania de la Macarena there is a tributary of the Guayabero River called the "Liquid Rainbow." While it isn't made from rainbows exactly, for a very short season the river with the majestic name of Caño Cristales flows with all the colors of the rainbow.
Carved from prehistoric black rocks with bright yellow sands in its riverbed, green mosses thrive in the river system, contrasting with the bright blue (crystal, for its namesake) waters that are so clear because of their lack of nutrients. But the color that appears for a short period of time and really draws the rainbow together is the indigenous red algae, Macarenia clavigera (Podostemaceae), that covers the bottom of the river from the end of July through November. These colors together create a riverscape that is unique to the world.
The Serranía de la Macarena, where the river is located, is on the border of three large ecosystems: the Andes, the Eastern Llanos, and the Amazon rain forest. While these ecosystems all boast a vast biodiversity, in the river itself plant and animal life struggle with the lack of nutrients and have therefore developed diverse adaptations, which you can see if you're ever lucky enough to visit "the most beautiful river in the world"!