A team of researchers at Universidad de Costa Rica and the Universidad Nacional discovered that the blue water of Rio Celeste is actually an optical illusion rather than a chemical phenomenon (as previously believed).
The reason we see the water in such a bright blue is because of a white substance that coats the rocks at the bottom of the river bed. The substance is a mineral composed of aluminum, silicon, and oxygen that when present in sizes as large as 566 nm (as they are in Rio Celeste) results in the electric blue color we see.
