<P> Long before the arrival of the Spanish, the lake system had been shrinking due to climate change . Warmer temperatures had increased evaporation and reduced rainfall in the area so that the lakes' waters were shallow at about five meters (16 ft) deep as early as the Tlapacoya culture, around 10,000 BCE . During the Aztec Empire, the northern lakes were inaccessible by canoe during the dry season from October to May . </P> <P> For two thousand years, humans have been interfering with and altering the hydraulic conditions of the valley, especially in the lakes region . The Aztecs built dikes for flood control and to separate the saline water of the northern lakes from the fresh water of the southern ones . After the destruction of Tenochtitlan in 1521, the Spaniards rebuilt the Aztec dikes but found they did not offer enough flood protection . </P> <P> The arrival of the Spanish and subsequent efforts to drain the area for flood control was a major infrastructure project, called the desagüe, was pursued the entire colonial period . </P> <P> The idea of opening drainage canals first came about after a flood of the colonial city in 1555 . The first canal was begun in 1605 to drain the waters of Lake Zumpango north through Huehuetoca which would also divert waters from the Cuautitlán River away from the lakes and toward the Tula River . This project was undertaken by Enrico Martínez and he devoted 25 years of his life to it . He did succeed in building a canal in this area, calling it Nochistongo, leading waters to the Tula Valley, but the drainage was not sufficient to avoid the Great Flood of 1629 in the city . Another canal, which would be dubbed the "Grand Canal" was built parallel to the Nochistongo one ending in Tequixquiac . The Grand Canal consists of one main canal, which measures 6.5 meters (21 ft) in diameter and 50 km (30 mi) long . The drainage project was continued after independence, with three secondary canals, built between 1856 and 1867 . During the presidency of Porfirio Díaz (r . 1876 - 1911) again became a prioirity. Porfirio Díaz completed all of it officially in 1894 although work continued thereafter . Despite the Grand Canal's drainage capacity, it did not solve the problem of flooding in the city . </P>

Which amerindian group lived in the valley of mexico the site of modern day mexico city