Cuicocha, Crater lake in Imbabura Province, Ecuador

Cuicocha is a crater lake in Imbabura Province formed inside a volcanic caldera. Two islands of volcanic rock emerge from the water, which reaches depths of around 200 meters in its deepest areas.

A massive phreatic eruption about 3,100 years ago produced some 5 km³ of pyroclastic flow and blanketed the surrounding area in ash up to 20 cm deep, leaving the 3 km-wide caldera. Volcanic activity continued until around 650 CE, and eruptions from Cuicocha together with Cotacachi, Imbabura, Mojanda and Cayambe built the fertile soil of the Otavalo Valley. In October 2022 the IUGS listed the Cotacachi-Cuicocha volcanic complex among its 100 geological heritage sites.

The Kichwa name means "guinea pig lake", after the guinea pig shape of the larger island, Teodoro Wolf; the Spanish source also gives Kuychi Kucha, "lake of the rainbow". On the second day of Inti Raymi, at each summer solstice, shamans use the lake for ritual cleansing and purification baths.

Cuicocha sits at 3,068 m at the southern end of the Cotacachi-Cayapas Ecological Reserve, 190 km north of Quito. The caldera rim is extremely steep, so paths follow the edge rather than descending to the water. The lake has no known outlet and is highly alkaline. Both islands, Yerovi and Teodoro Wolf, are off-limits to visitors.

The lake has no known outlet, is highly alkaline and holds little life; its deepest point reaches 200 m. In 1974 a census counted 44 silvery grebes, birds that live around the reeds and feed on small fish, frogs, crayfish and insects. In October 2022 the IUGS listed the Cotacachi-Cuicocha volcanic complex among 100 geological heritage sites worldwide.