Between the
Pleistocene epoch and the
last glacial period, the lake occupied the entire Mexico Valley. Lake Texcoco reached its maximum extent 11,000 years ago with a size of about and over deep. When the lake's water level fell it created several paleo-lakes that would connect with each other from time to time. At the north in the modern community of San Miguel Tocuilla there is an important
paleontological field where many fossilized Pleistocene
fauna have been discovered. The lake was primarily fed by snowmelt from nearby mountain glaciers when the Mexico Valley had a temperate climate. Between 11,000 and 6,000 years ago, the climate naturally warmed and snowfall in central Mexico became less prevalent. This caused the water level of the lake to drop over the next several millennia. Remnants of the ancient shoreline that Lake Texcoco had from the last glacial period can be seen on some slopes of
Mount Tlaloc as well as mountains west of Mexico City. The disarticulated remains of seven
Columbian mammoths dated between 10,220 ± 75 and 12,615 ± 95 years (
BP) were found, suggesting human presence. It is believed that the lake may have disappeared and subsequently re-formed at least 10 times in the last 30,000 years. Agriculture around the lake began about 7,000 years ago, with humans following the patterns of periodic inundations of the lake. Several villages appeared on the northeast side of the lake between 1700 and 1250 BC. By 1250 BC the identifying signs of the
Tlatilco culture, including more complex settlements and a stratified social structure, are seen around the lake. By roughly 800 BC
Cuicuilco had eclipsed the Tlatilco cultural centers and was the major power in the Valley of Mexico during the next 200 years when its famous conical
pyramid was built. The
Xitle volcano destroyed Cuicuilco around AD 30, a destruction that may have contributed to the rise of
Teotihuacan. After the fall of Teotihuacan, AD 600–800, several other city-states appeared around the lake, including Xoloc,
Azcapotzalco,
Tlacopan, Coyohuacan, Culhuacán, Chimalpa, and Chimalhuacán – mainly from
Toltec and
Chichimeca influence. None of these predominated and they coexisted more or less in peace for several centuries. This time was described as a Golden Age in Aztec chronicles. By the year 1300, however, the Tepanec from Azcapotzalco were beginning to dominate the area.
Tenochtitlan According to a traditional story, the
Mexica wandered in the deserts of modern Mexico for 100 years before they came to the thick forests of the place now called the Valley of Mexico.
Tenochtitlan was founded on an
islet in the western part of the lake in the year 1325. Around it, the
Aztecs created a large
artificial island using a system similar to the creation of
chinampas. To overcome the problems of drinking water, the Aztecs built a system of
dams to separate the salty waters of the lake from the rain water of the
effluents. It also permitted them to control the level of the lake. The city also had an inner system of channels that helped to control the water. The Aztec ruler
Ahuitzotl attempted to build an aqueduct that would take fresh water from the mainland to the lakes surrounding Tenochtitlan. The aqueduct failed, and the city suffered a major flood in 1502. During
Hernán Cortés's siege of Tenochtitlan in 1521, the dams were destroyed and never rebuilt, so
flooding became a big problem for the new
Mexico City built over Tenochtitlan.
Artificial drainage Mexico City suffered from periodic floods; in 1604 the lake flooded the city, with an even more severe flood following in 1607. Under the direction of
Enrico Martínez, a drain was built to control the level of the lake, but in 1629 another flood kept most of the city covered for five years. At that time, it was debated whether to relocate the city, but the Spanish authorities decided to keep the existing location. , December 1855 Eventually the lake was drained by the channels and a
tunnel to the
Pánuco River, but even that could not stop floods, since by then most of the city was under the
water table. The flooding could not be completely controlled until the twentieth century. In 1967, construction of the
Drenaje Profundo ("Deep
Drainage System"), a network of several hundred kilometers of tunnels, was completed, at a depth between . The central tunnel has a diameter of and carries rain water out of the basin. The
eastern discharge tunnel was inaugurated in 2019. The ecological consequences of the draining were enormous. Parts of the valleys were turned semi-arid, and even today Mexico City suffers from lack of water. Due to
overdrafting that is depleting the aquifer beneath the city, Mexico City is estimated to have
sunk 10 meters (33 feet) in the last century. Furthermore, because soft lake sediments underlie most of Mexico City, the city has proven vulnerable to
soil liquefaction during earthquakes, most notably
in the 1985 earthquake when hundreds of buildings collapsed and thousands of people died. The term "Texcoco Lake" now refers only to a big area surrounded by
salt marshes east of Mexico City, which covers part of the ancient lake bed. There are also small remnants of the lakes of
Xochimilco,
Chalco, and
Zumpango. Several species indigenous to the lake are now extinct or endangered (e.g.
axolotls). == Restoration and conservation ==