Lake Titicaca, Bolivia/Peru

Titicaca (in the hispanicized spelling) or Titiqaqa (Quechua) is a lake in the Andes on the border of Peru and Bolivia. By volume of water, it is the largest lake in South America. Lake Maracaibo has a larger surface area, but it is considered to be a large brackish bay due to its direct connection with the sea.

It is often called the highest navigable lake in the world, with a surface elevation of 3,812 metres (12,507 ft). Although this refers to navigation by large boats, it is generally considered to mean commercial craft. For many years the largest vessel afloat on the lake was the 2,200-ton, 79-metre (259 ft) SS Ollanta. Today the largest vessel is probably the similarly sized, but broader, train barge/float Manco Capac, operated by PeruRail (berthed, as of 17 June 2013, at 15°50′11″S 70°00′53″W, across the pier from theOllanta). At least two dozen bodies of water around the world are at higher elevations, but all are much smaller and shallower.

The lake is located at the northern end of the endorheic Altiplano basin high in the Andes on the border of Peru and Bolivia. The western part of the lake lies within the Puno Region of Peru, and the eastern side is located in the Bolivian La Paz Department.

The lake is composed of two nearly separate sub-basins connected by the Strait of Tiquina, which is 800 m (2,620 ft) across at the narrowest point. The larger sub-basin, Lago Grande (also called Lago Chucuito), has a mean depth of 135 m (443 ft) and a maximum depth of 284 m (932 ft). The smaller sub-basin, Wiñaymarka (also called Lago Pequeño, "little lake"), has a mean depth of 9 m (30 ft) and a maximum depth of 40 m (131 ft). The overall average depth of the lake is 107 m (351 ft).

Five major river systems feed into Lake Titicaca. In order of their relative flow volumes these are Ramis, Coata, Ilave, Huancané, and Suchez. More than twenty other smaller streams empty into Titicaca, and the lake has 41 islands, some of which are densely populated.

Having only a single season of free circulation, the lake is monomictic, and water passes through

Lago Huiñaimarca and flows out the single outlet at the Río Desaguadero, which then flows south through Bolivia to Lake Poopó. This only accounts for about 10% of the lake's water balance. Evapotranspiration, caused by strong winds and intense sunlight at high altitude, balances the remaining 90% of the water input. It is nearly a closed lake.

Since 2000 Lake Titicaca has experienced constantly receding water levels. Between April and November 2009 alone the water level dropped by 81 cm (32 in), reaching the lowest level since 1949. This drop is caused by shortened rainy seasons and the melting of glaciers feeding the tributaries of the lake. Water pollution is also an increasing concern because cities in the Titicaca watershed grow, sometimes outpacing solid waste and sewage treatment infrastructure.

The cold sources and winds over the lake give it an average surface temperature of 10 to 14 °C (50 to 57 °F). In the winter (June – September), mixing occurs with the deeper waters, which are always between 10 to 11 °C (50 to 52 °F).