The Lácar Lake is a lake of glacial origin in Neuquén Province, Argentina. It is enclosed in a mountain range of the Andes, at 630 m above mean sea level, approximately at 40°11′S 71°32′W / 40.183°S 71.533°W. The area around the lake is mostly uninhabited, except for the small city of San Martín de los Andes on its northeastern coast.
The lake has a surface area of 55 km² and a mean depth of 167 m, with a maximum of 277 m. Its catchment basin comprises 1,048 km². Like many Andean Argentine lakes, it drains across Chile and into the Pacific Ocean, in this case via the Huahum River that flows through Huahum Pass in the Andes.
As the northernmost lake on the eastern side of Andes that drains to the Pacific the lake and his catchment basin was claimed by Chile until 1902 based on an interpretation of the Boundary treaty of 1881 between Chile and Argentina.