Presa Miguel Alemán

The lake behind the Miguel Alemán Dam, also called the Temascal Dam, fills the valleys of the Río Tonto in northern Oaxaca, in the Papaloapan basin at the foot of the Sierra Mazateca. At about 47,800 hectares it is a huge body of water, and a channel links it to the Cerro de Oro reservoir on the Río Santo Domingo; downstream, the Tonto and the Santo Domingo meet to form the Papaloapan.

The dam was built to tame the floods of the lower Papaloapan, which had a history of devastating floods. Work began in 1949 under President Miguel Alemán, and Temascal was founded on 14 June 1950 at the spot chosen for the 830 m dam wall. The water drowned old San Miguel Soyaltepec, founded around 1500, and forced about 22,000 Mazatec people off their land; many were resettled 50 to 200 km away. Part of the old town survives as an island, Viejo Soyaltepec, and other summits such as Isabel María became islands too.

Mazatec and Chinantec families now live around the shore in San Pedro Ixcatlán, San Miguel Soyaltepec and San José Independencia. Commercial fishing lands about 700 tonnes a year of catfish, tilapia and carp, and the northwest shore and islands are a nature reserve. On the Ixcatlán side lies the area known as Mil Islas: dozens of islets that show or vanish with the water level, served by the community-run Cerro Quemado ecotourism centre with its lookouts, cabins, the Cabeza de Tilpan cave and a seasonal waterfall about 20 m high.