section_path: Geography/Hydrography
section_name: Hydrography
paragraph_text: Hydrography
  
  The Tietê River and its tributary, the Pinheiros River, were once important sources of fresh water and leisure for São Paulo. However, heavy industrial effluents and wastewater discharges in the later 20th century caused the rivers to become heavily polluted. A substantial clean-up program for both rivers is underway. Neither river is navigable in the stretch that flows through the city, although water transportation becomes increasingly important on the Tietê river further downstream (near river Paraná), as the river is part of the River Plate basin.
  
  No large natural lakes exist in the region, but the Billings and Guarapiranga reservoirs in the city's southern outskirts are used for power generation, water storage and leisure activities, such as sailing. The original flora consisted mainly of broadleaf evergreens. Non-native species are common, as the mild climate and abundant rainfall permit a multitude of tropical, subtropical and temperate plants to be cultivated, especially the ubiquitous eucalyptus.
  
  The north of the municipality contains part of the 7,917 hectares (19,560 acres) Cantareira State Park, created in 1962, which protects a large part of the metropolitan São Paulo water supply. In 2015, São Paulo experienced a major drought, which led several cities in the state to start a rationing system.