Caño Cristales’ various colors are the result of Macarenia clavigera, a rare species of aquatic plant that spans the length of the river (via Gentside). The plants change color depending on how much sunlight they receive, which is determined by the height and speed of the water. It is therefore not uncommon for the plants to be completely colorless if sunlight is too inaccessible. Macarenia Clavigera is also an exceptionally delicate plant; its transparent leaves give the water an almost painted appearance (via the BBC). 

This makes them easily damaged by major disturbances in the water and, unfortunately, human visitors initially tended to trample them while swimming. Once a tourist industry was established around the site, regulations were put in place that cut down the number of visitors, prohibited any chemicals such as bug spray, and limited how many people could swim at one time. Regardless, The River of Five Colors stands out as one of Colombia’s most popular natural attractions, drawing thousands of tourists every year (via CNN).