Often referred to as the river of five colors, Caño Cristales is a natural wonder not to miss. For most of the year visitors can observe the pale, green algae below the calm waters. But once a year, between the wet and dry seasons, when the water is just right, a unique species of plant that grows on the river bed—called Macarenia clavigera—turns a bright red, making a rainbow of colors along with the bits of yellow, green sand and blue water.