The canals would remain a part of the borough until the mid-20th century. Efforts to preserve the system began in 1920, when ejido owners turned over land to construct new ones. In the 1930s, many of the barrios of Iztapalapa were still marked by canals and still grew vegetables, fruits and flowers. Major traffic was confined mostly to the Canal Nacional on the borough's border. However, groundwater pumping started in the 1950s lowered water tables and began the process of destroying the rest of the canals, and most of the chinampas along with them.