Formed by the confluence of two smaller rivers, the is a bright blue river in Costa Rica that winds through the lush rainforest of . The vibrant blue color occurs at the confluence of two smaller rivers, Sour Creek and Good View River, a spot that has earned the name El Teñidor (‘The Dyer’).

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The color is , according to Amusing Planet, a phenomenon caused by the presence of large particles of a mineral called aluminosilicate in the river’s water, which reflect sunlight, giving rise to the vibrant blue hue.

Aluminosilicate is found in the Good View River but the , reports Amusing Planet. It is only when Good View River mixes with Sour Creek, a stream that has highly acidic water due to volcanic activity, that the color occurs. When the two waters mix, a drop in pH occurs, causing aluminosilicate particles to aggregate and enlarge enough for the in Rio Celeste.

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There are two trails of varying difficulty that lead to the blue river of Rio Celeste. More experienced hikers can take the through the rainforest, past thermal hot springs and a blue lagoon; while visitors can venture along the shorter (one mile) path from the park entrance directly to the Rio Celeste Waterfall.

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