Pedestrians walk through a bridge over the polluted Tiete River in Pirapora do Bom Jesus, about 50km away from Sao Paulo, Brazil. Tiete is the main river of Sao Paulo State and the pollutant foam is related to the low flow of water and the presence of untreated sewage, according to Sao Paulo's State Environment Department. Photo: Xinhua

A car runs through a bridge over the polluted Tiete River in Pirapora do Bom Jesus, about 50km away from Sao Paulo, Brazil. Tiete is the main river of Sao Paulo State and the pollutant foam is related to the low flow of water and the presence of untreated sewage, according to Sao Paulo's State Environment Department. Photo: Xinhua

Photo taken on June 24, 2015 shows a general view of the polluted Tiete River in Pirapora do Bom Jesus, about 50km away from Sao Paulo, Brazil. Tiete is the main river of Sao Paulo State and the pollutant foam is related to the low flow of water and the presence of untreated sewage, according to Sao Paulo's State Environment Department. Photo: Xinhua

A woman walks through a bridge over the polluted Tiete River in Pirapora do Bom Jesus, about 50km away from Sao Paulo, Brazil. Tiete is the main river of Sao Paulo State and the pollutant foam is related to the low flow of water and the presence of untreated sewage, according to Sao Paulo's State Environment Department. Photo: Xinhua