The lake was formed approximately 2–3 million years ago due to faulting and subsequent damming of the Cabriales River. The lake has been completely dry during several discrete periods of its geologic history. Alexander von Humboldt visited the lake in 1800. He documented the negative impact of the surrounding population's land cultivation on the ecosystem. Deforestation and water diversion for irrigation led to dramatically reduced water levels. Lake Valencia is where Humboldt developed his conception of anthropogenic climate change. He later wrote:
When forests are destroyed, as they are everywhere in America by the European planters, with an imprudent precipitation, the springs are entirely dried up, or become less abundant, The beds of the rivers remaining dry during a part of the year, are converted into torrents, whenever great rains fall on the heights. The sward and moss disappearing from the brush-wood on the sides of the mountains, the waters falling in rain are no longer impeded in their course: and instead of slowly augmenting the level of the rivers by progressive filtrations, they furrow during heavy showers the sides of the hills, bear down the loose soil, and form those sudden inundations that devastate the country.
Since 1976 Lake Valencia water levels have risen due to diversion of water from neighboring watersheds—it currently acts as a reservoir for the surrounding urban centers.
Ecology
The lake suffers from algal blooms caused by continual influx of untreated wastewater from the surrounding urban, agricultural, and industrial land uses. This contributes to ongoing eutrophication, contamination, and salinization of the lake. Despite its picturesque location between the Cordillera de la Costa to the north and the Serrania del Interior to the south, Lake Valencia's poor water quality limits opportunities for tourism and recreational activities. Due to pollution and other human induced changes, almost 60% of the native fish species in the lake were lost between 1960 and 1990. Among the fish in the lake is the diamond tetra, which is commonly kept in aquaria, while two species of catfish, Lithogenes valencia and Pimelodella tapatapae are entirely endemic to the lake basin. A Lake clean up scheme with finance from IDB has been described along with information on pollution loads, reuse opportunities and wastewater collection and treatment infrastructure which was installed between 1991 and 2002.
