Lake Titicaca is the largest freshwater lake in South America, located on the border between Peru and Bolivia between the two snowy mountain ranges of East and West Cordillera in the central Andes. The lake is 8,372 km² wide, including both the deep main basin (Lago Mayor) and the shallow sub-basin (Lago Pequeno), and its altitude (3,812 m) is unrivalled among large lakes of this size class in the world.

The distribution of old coastal terraces indicates that a huge body of water reaching as far south as the Uyuni Depression once existed during an inter-glacial period of the Pleistocene, but the lake's size has been greatly reduced due to the increasing aridity of climate and the formation of an effluent stream. The water of Titicaca is now drained via the Rio Desaguadero into Lago Poopo, which, however, has no outlet to the sea.

The whole catchment area on the high plateau of Altiplano remains almost treeless, and is covered by coarse grasses with scattered fields of potato, barley, quinoa (Chenopodium quinoa) and the other local crops. The lake is fringed by a swampy zone of totora (Scirpus tatora), which is indispensable for the life of inhabitants on the shore, furnishing materials for the famous reed-boats and floating gardens where they grow potatoes.

The line between Puno (Peru) at the northwestern end of the lake and Guaqui (Bolivia) on the southwestern shore is an important shipping route for Bolivia. an inland country without seaside territory. Recent development of cities with manufacturing industry and a few sightseeing sites are going to affect the quality of the lake water to a certain extent.