December 13, 2022, 4:40 pm | Read time: 4 minutes
In Costa Rica’s national park at the foot of the Tenorio Volcano lies one of the country’s greatest natural wonders. The Rio Celeste, which shines in an almost otherworldly blue. For a long time, scientists from around the world puzzled over the reason for the unusual color of the water. Then they found a surprising explanation.
It’s no secret that nature plays a big role in the small Central American country of Costa Rica. But in the national park at the foot of the Tenorio Volcano, there’s a place that seems particularly enchanting–almost as if it were not real, but from a fairy tale. We’re talking about the Rio Celeste, a river with a unique color. Its water shines in an almost unnaturally blue hue. And that’s exactly what has made it one of the country’s biggest tourist attractions.
Over a stretch of fourteen kilometers, the water of the Rio Celeste has this extremely unusual coloration. Celeste translates literally from Spanish as “sky blue,” but in some places, it almost seems neon. For many years, scientists from around the world could only speculate about the origin of this unique feature. A popular hypothesis was that the color was caused by metals and/or minerals in the water. It wasn’t until 2013 that a local research team discovered the true reason.
Why does the river glow so supernaturally blue?
The scientists from the Universidad de Costa Rica (UCR) and the Universidad Nacional (UNA) were particularly puzzled by one detail. The Rio Celeste is formed by the confluence of two other bodies of water, the Rio Quebrada Agria and the Rio Buena Vista. Both have no coloration at all; their water is completely clear. Only at the point where they merge into the Rio Celeste does the otherworldly blue appear, as if by a (natural) miracle. Samples from the sky-blue river led to the next surprise: Once water was taken from it, it lost its color properties and became crystal clear as well.
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After further investigations, the researchers soon concluded: The phenomenon that colors the Rio Celeste sky blue could not be chemical. Rather, it is a kind of optical illusion created by the human eye. And this, in turn, is caused by the sunlight itself. In sunlight, all the spectra of the color palette are present–just think of a rainbow. Normally, water absorbs sunlight without reflecting a particular color. However, in the Rio Celeste, it reflects the blue shades for a very specific reason, so that the river appears to the viewer in this special hue.
Swimming in the wonder river
But why does this phenomenon occur exactly here? During their research, the scientists discovered a whitish substance in the riverbed of the Rio Celeste that covered the stones and the ground. These are particles of a mineral called aluminum silicate. It consists of aluminum, silicon, and oxygen and is responsible for the unique way sunlight is reflected in the river. This, in turn, is related to the size of the particles, which are in the nanometer range. If the particles were larger or smaller, they would likely reflect a different color.
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The countless tourists who visit the Rio Celeste each year probably prefer to believe a local legend that seeks to explain the river’s color. According to the legend, God dipped his brushes in the water here after he finished painting the sky. Today, numerous activities await vacationers around the river. You can hike or ride along its banks. Rafting is also possible, as well as a swim in the beautiful blue. It’s not surprising that the water is also said to have healing powers.
Anyone who searches for “Rio Celeste Tours” on Google will quickly find numerous results. On Tripadvisor, users are full of praise for this unique natural wonder. “Definitely one of the most beautiful places I’ve ever seen with my own eyes,” says one. Another comments, “The entire national park is breathtaking. A must-see when in Costa Rica!” A third adds, “This place is truly magical. The pictures don’t lie; it really looks like that.”