Lake Poopó is a large saline lake located in a shallow depression in the Altiplano Mountains in Bolivia at an altitude of approximately 3,700 meters. Because the lake is long and wide (90 km by 32 km) it makes up the eastern half of the Oruro Department, a mining region in southwest Bolivia. The permanent part of the lake body covers approximately 1,000 km². The lake receives most of its water from the Desaguadero River which links Lake Poopó with Lake Titicaca at the north end of the Altiplano. Since the lake lacks any major outlet and has a mean depth of no more than 3 m, the surface area varies greatly.

The lake has been designated as a site for conservation under the Ramsar Convention. Lake Poopó gets the majority of its water (roughly 92%) from the Desaguadero River which enters the lake at the north end. There are numerous smaller inlets along the eastern shore of the lake, many of which are dry most of the year. At times of very high water levels, Poopó is connected to the salt desert Salar de Coipasa in the west. A minor outlet also leads to Salar de Uyuni in the far south of the Altiplano, but as the lake lacks any major outlet it is classified as an endorheic basin.

When the water level of Lake Titicaca drops below 3,810 m, the flow of River Desaguadero is so low it can no longer compensate for the massive water losses due to evaporation from the surface of Lake Poopó. At this point, the lake volume begins to decrease. At its maximum in 1986, the lake had an area of 3,500 km². During the years that followed, the surface area steadily decreased until 1994 when the lake disappeared completely. The time period between 1975 and 1992 is the longest period in recent times with a continuous existence of a water body.

Lake Titicaca basin's drainage system, for the most part, is able to provide Titicaca with enough water to retain its status as a freshwater lake although its evaporation rate is so high. The water of Lake Poopó is highly saline. The salinity is a result of the endorheic nature of the hydrolocial system on the Altiplano, which allows all weathered ions to remain in the system. The salinity of Lake Poopó is further enhanced by the lack of outlet, the arid climate and the high evaporation from the lake surface.

In the northern end of Lake Poopó there is a dilution with freshwater from River Desaguadero. This results in a salt gradient of higher values towards the south. The salinity varies with water volume. During October – November 2006 the salinity in the north end of the lake varied between brackish and saline (15-30,000 mg/l). In the south end of the lake the water was classified as a brine (105,000- 125,000 mg/l). The water type is a 4-2 Na-(Mg)-Cl-(SO4).

Geological sources of NaCl such as halite and feldspars are present in the drainage area. These could also contribute to the salinity of Lake Poopó. The lake body is situated on top of Cenozoic deposits, consisting mainly of unconsolidated material. These sediments are the remains of extensive prehistoric lakes, which covered the Altiplano during at least five glaciation periods.

There is a long tradition of mining in the Poopó basin. Extraction of metals began already in the 13th century in order to support the Inca army. After the Spanish colonization in the 16th century, the mining operations became more large scale. At this point the region got its current identity as one of the mining centres of Bolivia.