Celeste of Costa Rica, the great optical illusion

Until a few years ago, the Celeste River, a 14-kilometer “pond” located in the province of Alajuela (Costa Rica), was a complete mystery for the researchers. They could not understand why their waters had such an unusual turquoise color. What kind of “magic” produced this optical illusion?

The truth is that theories about the turquoise color of the river had circulated in the scientific community for years, although no one had managed to provide enough evidence to solve this natural enigma. Some claimed that the unusual coloration was due to high copper levels, but tests revealed that there was no copper in the water.

Others said it was due to chemicals such as calcium carbonate and sulfur, or even some related to the proximity of the Tenorio Volcano River. In general, most were so convinced that some kind of mysterious chemical reaction was turning turquoise water, that they did not even value the possibility of an optical illusion.

Outside of “the scientific”, there was no shortage of beliefs based on myths and legends. The most repeated was the local legend that said the waters of the river had that color because when God finished painting the sky, washed the brushes in the water of Celeste.

Until 2013. Then a group of researchers from the University of Costa Rica and Nacional arrived to take a series of water samples from both the Celeste River and its two tributaries, Quebrada Agria and Río Buena Vista.

Here they found the first differences. While the waters of Rio Celeste were a vibrant turquoise color, the samples they collected in their test tubes were completely transparent. How?

To fully understand the mystery of Rio Celeste, it is important to know that Sour Creek and Río Buena Vista, the two rivers that converge to create this fascinating body of water, are completely transparent, and the analysis revealed no unusual chemical reactions. What is even more interesting is that Rio Celeste is turquoise only for a stretch of 14 kilometers, after which its waters become transparent. In fact, the unusually colored section of the river is known as El Teñidero.

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