Lago de Chapala

Lake Chapala is Mexico's largest natural freshwater lake: about 80 km from east to west, up to 18 km wide and roughly 1,100 km² in area, lying at 1,520 metres above sea level about 45 km southeast of Guadalajara. Some 86% of the water surface is in Jalisco and the rest in Michoacán. For its size it is remarkably shallow, about 10 metres at most, and carbon dating of wood in its sediments puts its age at around 38,000 years.

The Lerma River feeds it along with the Zula, Duero and Huaracha, and the Río Grande de Santiago flows out of it, although with less water arriving down the Lerma almost nothing has left by that outlet for decades. Since the 1950s the lake has been Guadalajara's main water source, and it now supplies about 60% of the water reaching the metropolitan area. Pumping, pollution carried down the Lerma, silting and evaporation have lowered its level more than once, and water hyacinth covers patches of it in some seasons. In February 2009 it was listed as a Ramsar wetland of international importance.

The Jalisco shore belongs to the municipalities of Chapala, Jocotepec, Poncitlán, Ocotlán, Jamay, Tuxcueca and Tizapán el Alto; on the Michoacán side are Cojumatlán de Régules, Venustiano Carranza and Briseñas. The north shore between Chapala, Ajijic and San Juan Cosalá has drawn visitors since the 19th century, and since the 1950s one of the largest colonies of American and Canadian retirees in Mexico, estimated at around 30,000 people. The pre-Hispanic name is linked to Chimaloacán, while Chapala is usually traced to Chapatla or Chapatlán, after a local lord called Chapa.

There are three islands: Mezcala, the largest; tiny Isla Menor beside it; and Isla de los Alacranes. Mezcala was the stronghold of lakeshore insurgents who held out against royalist attacks from 1812 until an armistice in November 1816, under which their leader, the priest Marcos Castellanos, was pardoned, and the ruins of the fort and later prison still stand there. In winter migratory birds arrive from the United States and Canada, above all American white pelicans, which gather in their thousands at Petatán Island on the Michoacán side. The lake is home to endemic fish such as several Chirostoma charal silversides and the Chapala chub, though a number of native species are threatened.