The Aztec region of Mesoamerica, called Anáhuac, contained a group of five connected lakes. The largest of them was Lake Texcoco. The Aztec built their capital city, Tenochtitlan, on Lake Texcoco. Built on two islands, the area was extended using chinampas—small, artificial islands created above the waterline that were later consolidated. Tenochtitlan eventually reached an area of more than 13 square kilometers (five square miles). Causeways that doubled as dikes connected the island to the mainland and separated freshwater from salt water, protecting the chinampas.
See:
https://education.nationalgeographic.org/resource/tenochtitlan/ ↗️