Laguna de Alchichica

Alchichica is a crater lake, a maar, beside the village of San José Alchichica in Tepeyahualco de Hidalgo municipality, on the Oriental basin of the Puebla highlands near the Veracruz state line. The water fills a volcanic crater 1.7 km long and 1.4 km wide at 2,345 metres above sea level, about 65 metres deep at its deepest and close to 39 metres on average. It is salty and alkaline, around 13 grams of salt per litre and rich in magnesium; on sunny days it turns emerald green and smells faintly of sulphur.

The striking feature is the band of white rock that circles nearly the whole shore like a reef. These are stromatolites, carbonate structures built by communities of cyanobacteria. The aragonite-rich ones at the waterline are roughly 1,100 years old, and the spongier mounds further in about 2,800. The lake also shelters species that live nowhere else: the Alchichica axolotl (Ambystoma taylori), under special protection, the Alchichica silverside (Poblana alchichica), listed as threatened, plus two crustaceans and a diatom of its own. It lies inside the state protected area Lagos de Tepeyahualco y Guadalupe Victoria, and in 2022 Puebla's environment ministry and the national water commission stopped an open-water swim race that had not asked permission to use it.

On the shore there are restaurants serving Puebla food, a hotel with a restaurant at the entrance and kayak and boat rental. You can walk around the crater rim and, on a clear day, see Cerro Pizarro and Pico de Orizaba. Locals tell of mermaids, a bottom nobody has reached, whirlpools and lights that slip in and out of the water at night. About 10 km south lie La Preciosa and Quechulac, two more crater lakes of the same basin.