Titicaca (tētēkäˈkä) [key], lake, c.3,200 sq mi (8,290 sq km), 110 mi (177 km) long, and c.900 ft (270 m) deep at at its deepest point, in the Andes Mts., on the Bolivia-Peru border; second largest freshwater lake in South America and the world's highest large lake (c.12,500 ft/3,810 m above sea level). The lake is divided into two basins by the Strait of Tiquina. Fed by many short mountain streams, the lake is drained by the Desaguadero River to Lake Poopó. A center of indigenous life from pre-Inca times, the shores of Titicaca are crowded with native villages and terraced fields, which are a major source of subsistence crops for the largely barren highland region. The almost constant temperature of the water (51°F/11°C) modifies the climate and makes possible the growing of potatoes and grains at the high altitude. Native balsas, small flat-bottomed reed boats with reed sails, dot the lake and are used for commerce and fishing. Steamer service connects the lake ports of Guaqui, Bolivia, and Puno, Peru. On the lake near Puno, Uros live on floating islands made of reeds. Near the lake's southern shore is the pre-Inca ruin Tiahuanaco. In the lake are the islands of Titicaca and Coati, the legendary birthplace of the Incas, which contain ruins of past civilizations.