On the southern skirt of Cotacachi lies Lago Cuicocha, a lake which sits in the collapsed crater of a volcano that is part of the Cotacachi-Cuicocha complex. Around 3,500 years ago, the volcano collapsed and the water in the lake is said to be the remnants of the glacial cap that covered the Cuicocha dome. A subsequent eruption formed the two islands in the middle of the lake. Due to the continuing volcanic activity beneath the surface, the water remains at a temperature of 60 degrees F (16 degrees C), which is much higher than it should be at his elevation (over 10,000 feet).
Visitors to the lake can walk around the crater (3-6 hours, depending on ability and pace), take a boat ride out around the islands, or just visit and take in the scenery. There is a small museum at the entrance to the reserve which is worth a visit.