Lake Titicaca is the high-altitude lake between Peru and Bolivia that is the largest in South America by volume. It lies in the Andes at roughly 3,812 meters above sea level and is also South America's largest lake by surface area when Lake Maracaibo is classified as a tidal bay rather than a lake.
Titicaca is made up of two connected basins, Lago Grande and the smaller Wiñaymarka, joined by the Strait of Tiquina. More than 20 streams and rivers feed it, while evaporation is its main water loss; the Desaguadero River is its only major outflow. The lake contains dozens of islands, including the famous floating reed islands associated with the Uros people.
The phrase “highest navigable lake” is often attached to Titicaca, but it needs qualification: many smaller lakes sit at higher elevations, and the claim generally refers to navigation by sizable commercial vessels. Lake Baikal is much deeper and holds far more freshwater, but it is in Siberia, not South America.