Lake Texcoco
The lake was formed on a closed basin, with no drains, so it was salty. It occupied a great extension of the Anahuac valley, forming part of system of five lakes, between 2,270 and 2,750 meters above sea level, in the northern part of the Mexican highlands..Mexico-Tenochtitlan was founded on an islet in the western part of the lake in the year 1325. The aztecs create a big artifial island. To overcome the problems of drinking water, the aztecs build a system of dams to separe the salty waters of the lake, with the rain water of the afluents. It also permited them to control the level of the lake.
During the siege of Tenochtitlan, the dams were destroyed, and never rebuilded, son inundations became a mig problem for Mexico City.
Eventually the lake was drained by the German engineer, Heinrich Martin, in the 1607-8 AD, via channels and a tunnel to the PÃÂánuco River. Until it now occupies only a small area surrounded by salt marshes 2 1/2 mi (4 km) east of Mexico City. Because of this Mexico city is sinking at a rate of a few centimeters every year.