a body of water with a tree branch in the foreground

The enchanting blue hue of Río Celeste, located in the Tenorio Volcano National Park of Costa Rica, has long captivated visitors and scientists alike. It has been determined that the blue color is not due to a chemical composition but rather an optical illusion. When the two clear streams of Quebrada Agria and Río Buenavista converge at a point known as Teñidero, a physical reaction occurs. The riverbed's rocks are coated with a particular mineral composed of aluminum, silicon, and oxygen. These particles, specifically when they are around 566 nanometers in size, scatter sunlight in blue.