[2][3] The lake is of volcanic origin and was formed by a large basaltic lava flow from Volcán de San Diego in the San Diego volcanic field which blocked the Güija depression's original drainage.

The lake is surrounded by the volcanic cones of the Mita, San Diego and Cerro Quemado.

The Salvadoran side of the lake has several small isles: Teotipa, Cerro de Tule and Iguatepec, where a substantial number of pre-Columbian céramics[clarification needed] have been discovered since excavations started in 1924.

This site was added to the UNESCO World Heritage Tentative List on September 21, 1992, in the Mixed (Cultural + Natural) category.

[5] The lake and its surrounds has been designated an Important Bird Area (IBA) by BirdLife International because it supports significant populations of range-restricted birds, including white-bellied chachalacas, orange-fronted parakeets, Nutting's flycatchers and white-throated magpie-jays.