Things to do at Río Celeste

Río Celeste's turquoise water is not a paint stunt or a chemical spill: it is an optical effect. Two clear rivers meet at a point called the Tenidero, inside Tenorio Volcano National Park, and dissolved aluminosilicate particles grow there to a size that scatters blue light while letting other wavelengths pass through.

The colour is real, but it is weather-dependent. After heavy rain the rivers run high and cloudy with sediment, and the blue fades to brown or grey for a day or more, which is the single biggest source of visitor disappointment. La Fortuna to the trailhead is roughly 1 h 30 to 2 h by road.

Dry-season mornings (December to April) give the most reliable colour, before afternoon cloud and rain move in.