Lake Güija, Natural lake between Jutiapa Department and Santa Ana Department, Guatemala and El Salvador

Lake Güija lies at 430 m on the Guatemala–El Salvador border, 45 km² in area, of which about 32 km² (74%) is Salvadoran. It formed when a basaltic lava flow from Volcán de San Diego dammed the Güija depression. Two large peninsulas narrow the water, and the Salvadoran side holds the islands of Teotipa, Cerro de Tule and Igualtepec. It drains via the río Desagüe into the Lempa at the Guajoyo hydroelectric dam.

Lake Güija formed when a basaltic lava flow from the Volcán de San Diego blocked the drainage of the Güija depression. The Lenca, Xinca, Chʼortiʼ and Pipil lived around its shores; in the 16th century Diego García de Palacio noted two rocks used for sacrifice. Guatemala and El Salvador drew their border across the lake in 1938, and in 1957 they signed a water-sharing agreement.

The name Güija comes from Náhuat: huitsi (thorn) plus a (abundance), meaning "where thorns abound." On Igualtepeque, a peninsula that becomes an island in the rainy season, the beach holds over 80 petroglyphs, one of the region's main rock-art sites. A green stone plaque found by a diver in the lake is identified as an Early Classic Maya Lowlands object.

The lake lies at 430 m between Santa Ana department and Jutiapa department; the Salvadoran share is about 32 km², the Guatemalan about 26%. The Ostúa, Angue and Cusmapa feed it, and it drains via the Desagüe into the Lempa at the Guajoyo hydroelectric dam. Igualtepeque becomes an island when the lake rises in the rainy season, so reach it by boat then.

Igualtepeque, a peninsula that becomes an island when the lake rises in the rainy season, holds more than 80 boulders with petroglyphs, one of the region's main rock-art sites. A diver found a green stone plaque in the lake, identified as an Early Classic Maya Lowlands object.