The Billings dam is one of the largest and most important water reservoirs in the São Paulo Metropolitan Region. To the west, it limits with the watershed of Guarapiranga and, to the south, with the Mountain range of the Sea. Its main rivers and forming streams are the Great river or Jurubatuba. The dam was devised in the 1930s and 1940s by engineer Billings, one of the employees of the now defunct electric utility Light, hence the name. Initially, the dam was intended to store water to generate electricity for the Henry Borden hydroelectric plant in Cubatão. Due to the high population and industrial growth of the city of São Paulo and neighboring cities, it has occurred without planning, mainly during the decades of 1950 to 1970, Billings dam has small stretches polluted with domestic, industrial and heavy metal sewers. Only the Taquecetuba and Riacho Grande arms are used to supply drinking water by the sabesp, the waters of São Paulo, São Bernardo, Diadema and Santo André. In the past, even when there was an Environmental Law, there were several cases of subdivision and irregular sale of land near the dam, including the participation of politicians from some cities in the surrounding area. The dam is still degraded due to the construction of irregular houses and deforestation of the riparian forest.