Canals in the waters of Lake Xochimilco were initially created along with that of a kind of artificial agricultural plots called chinampas. Chinampas were invented by the pre-Hispanic peoples of the region around 1,000 year ago as a way to increase agricultural production. On the shallow waters of the lakes, rafts were constructed of juniper branches. Onto these rafts floating on the water, lakebed mud and soil were heaped and crops planted. These rafts, tied to juniper trees, would eventually sink and a new one be built to replace it. Over time, these sunken rafts would form square or rectangular islands, held in place in part by the juniper trees. As these chinampa islands propagated, areas of the lake were reduced to canals. These “floating gardens were an important part of the economy of the Aztec Empire by the time the Spanish arrived.[32][33][34] Today, only about 5,000 chinampas, all affixed to the lake bottom, still exist in their original form, surrounded by canals and used for agriculture. The rest have become solid ground and urbanized. In the center of Xochimilco, there are about 200 chinampas, covering an area of 1,800 hectares. However, one reason the number has decreased is that smaller chinampas have been combined to create larger ones.[30] While there are still those who maintain chinampas traditionally, and use them for agriculture, the chinampa culture is fading in the borough with many being urbanized, and being turned into soccer fields, and sites for housing and businesses.[27] The deterioration of many of these chinampas can be seen as their edges erode into the dark, polluted water of the canals.[33] The most deteriorated chinampas are located in the communities of Santa María Nativitas, Santa Cruz Acalpixca, San Gregoria Atlapulco and Ejido de Xochimilco. Together, these have a total of thirty eight illegal settlements. To repair a number of chinampas, the borough along with federal authorities, has reinforced forty two km of shoreline, of the 360 km (220 mi) that exist in the lake area. This involves the planting of juniper trees and the sinking of tezontle pylons into the lakebed.[27]