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What is a Blue River?

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A great spot for a dip along the blue river, Rio Penjamo

PART I – Posted June 2017

Let’s dive straight into the blue-waters of Costa Rica’s rivers. They are so blue it looks like it could be bottled and transported home. But unfortunately, that’s not possible!

There is a scientific explanation for blue-rivers. First off, the blue-color is an optical illusion created when clear water flows over a riverbed coated with special chemicals. Those chemicals are transported by the river from beneath the volcano and settle, coating the riverbed. At the source of the river the chemicals van be seen bubbling-up in the water and the fall and settle as they flow down-stream. Water flowing over these coated sections reflect the colors of the spectrum in manner permits the blue-rays to appear as the dominant color.

Much speculation over the cause of the brilliant blue-water continues today. The confusion arose when no one could explain what took place ont the renowned blue river, the Rio Celeste. Between the provinces of Alajuela and Guanacaste, two crystal-clear rivers flow in the Tenorio National Park and then join. Theses rivers, the Quebrada Agria (Broken Ravine) and Rio Buena Vista (River with a Good View) flow independently as crystal clear rivers before meeting at Teñidero (dye point). Here at Teñidero, these clear water rivers turn turquoise-blue and continue that way thereafter.

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The cause remained a mystery for many years, until the University of Costa Rica’s research confirmed no chemical or mineral concentrations made the water blue. Instead, the blue color is an optical phenomenon; the result of light rays being deflected by certain minerals coating the riverbed as sunlight passes through the water. The water acts as a prism and separates the sunlight into the seven primary-colors. Each color is a ray of light with its own specific wavelength. The seven colors combining to make white light are- violet; indigo; blue; green; yellow; orange; and red. Each color’s ray has a different wavelength; as explained in <Phillip Gibbs May 1997>.

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When light passes through certain mediums, some rays are amplified and others reduced. In the case of the Blue River’s water, the blue rays are amplified while others are reduced at the point where the water flows over those sections of the riverbed coated with the compound ‘aluminum-silicate’.