Lake Titicaca

Lake Titicaca is a big blue lake very high up in the mountains.

Peru is on one side and Bolivia is on the other. Snowy mountains stand nearby. People fish, farm and sail boats made of reeds.

Lake Titicaca sits high in the Andes mountains of South America, 3,810 meters above sea level. Britannica calls it the world's highest lake that big ships can sail on. The lake lies right on the border between two countries: Peru on the west and Bolivia on the east.

It covers about 8,300 square kilometers, which makes it the second largest lake in South America, after Lake Maracaibo. A narrow strait called Tiquina divides it into a big northern part and a smaller southern part. Forty-one islands rise from the water, and on the Bolivian side, snowy peaks of the Cordillera Real rise to more than 6,400 meters.

Britannica describes Lake Titicaca as the world's highest lake navigable to large vessels, at 3,810 m, astride the border between Peru (west) and Bolivia (east). Second in size in South America after Maracaibo, it covers some 8,300 km², extends 190 km from northwest to southeast and is 80 km across at its widest. The Strait of Tiquina divides it into a larger northwestern basin (Lake Chucuito in Bolivia, Lago Grande in Peru) and a smaller southeastern one (Lake Huiñaymarca in Bolivia, Lago Pequeño in Peru).

The lake averages 140 to 180 m deep, but its floor tilts sharply toward Bolivia, reaching its greatest recorded depth of 280 m off Isla Soto in the northeast. Its waters are clear and only slightly brackish (5.2 to 5.5 parts per thousand), with surface temperatures averaging 14 °C and falling to 11 °C at depth below a thermocline at 20 m. Forty-one islands rise from the lake; the largest, Isla del Sol, lies off the Copacabana Peninsula in Bolivia.

A big frog lives in Lake Titicaca and nowhere else.

It has lots of loose, wrinkly skin. The skin helps it take in air from the water. Little striped fish swim in the lake too. Reeds grow in the shallow water.

The Titicaca water frog lives in this lake and nowhere else. Zoo Berlin calls it the world's largest fully aquatic frog, up to 20 centimeters long. It has loose folds of skin that make it look as if it is wearing a baggy wetsuit, and those folds help it take in more oxygen from the cold water.

The frog is in trouble. The IUCN Red List, which tracks how endangered animals are around the world, lists it as Endangered. Zoo Berlin reports that its numbers have fallen by 80 percent in three decades, and it names threats including pollution, fishing and a deadly fungus disease. Britannica says the lake's native fish are mostly small killifish, often striped or barred with black, and a catfish; trout were added from 1939. In the marshy shallows grows totora, a tall reed that people use for building.

Britannica lists Titicaca's native fish as two species of killifish (Orestias) and a catfish (Trichomycterus); trout were introduced in 1939 and later. A large frog of the genus Telmatobius inhabits the shallows. Zoo Berlin identifies the Titicaca water frog (Telmatobius culeus) as the world's largest fully aquatic frog, up to 20 cm from head to rump, found naturally only in this lake; its baggy skin folds increase oxygen uptake in water at 3,810 m, where oxygen is scarce.

The zoo calls it the most endangered amphibian species in Bolivia; the IUCN Red List's global assessment (2019) lists it as Endangered, with a decreasing population. Jacques Cousteau reported thousands of the frogs on the lake bed in the 1970s, but numbers have since fallen by 80 percent; threats include the chytrid fungus, agricultural insecticides and pesticides, accidental capture and overfishing of their food. In 2015 many dead frogs were found across about 500 km² on the Bolivian side. A Bolivian Amphibian Initiative, run by the Museo de Historia Natural Alcide d'Orbigny and Fundación para las Ciencias, monitors wild frogs and breeds them in captivity for future reintroduction.

Some people live on floating islands made of reeds.

They make reed boats too. Long ago, a great city was built near the lake. Farmers grow potatoes and keep llamas and alpacas.

People have lived around Lake Titicaca for a very long time. Britannica says some Uru people still live on floating mats of dried totora reeds, and they and other lake people build boats called balsas from bundles of reeds tied together. Many Aymara farmers in the basin still farm stepped terraces older than the time of the Incas, growing barley, quinoa and potatoes, a crop that first came from the Altiplano.

At the southern end of the lake are the ruins of Tiwanaku. UNESCO explains that it was the capital of a powerful state that reached its peak between AD 500 and 900. Britannica says boats cross the lake between Puno, in Peru, and Guaqui, in Bolivia, and in 1862 the first steamship on the lake was carried up in pieces on the backs of mules.

Britannica writes that ruins on the lake bottom (where remains of a temple were found in 2000), on its shores and on its islands attest to one of the oldest civilizations of the Americas, with the chief site at Tiwanaku, Bolivia. UNESCO, which inscribed Tiwanaku in 2000, describes it as the capital of a powerful pre-Hispanic state that dominated a large area of the southern Andes and reached its apogee between AD 500 and 900, distinct from other pre-Hispanic empires of the Americas.

Aymara farmers in the basin still use stepped terraces that predate the Incas, growing barley, quinoa and potatoes; a barley field at 4,700 m near the lake was found to be the highest cultivated plot in the world, its grain never ripening but its stalks feeding llamas and alpacas. Ancient raised fields and ditches cover the lake plain, and this reclamation system has been revived in parts of Peru and Bolivia. Remnants of the Uru people live on floating mats of dried totora and, with other lake dwellers, build reed balsas. In 1862 the first steamer, prefabricated in England, was carried up by mule; vessels now cross from Puno to Guaqui, linked by rail to La Paz.