Pictures: Toxic Foam Chokes Brazil River

Pictures: Toxic Foam Chokes Brazil River

Toxic foam chokes Brazil's most polluted waterway, the Tietê River, on September 4 in the town of Pirapora do Bom Jesus (map).

The foam is caused mostly by untreated household runoff from nearby São Paulo, the biggest city in Brazil, according to Malu Ribeiro, water-program coordinator for the local environmental nonprofit SOS Mata Atlântica. The runoff flows directly into the river via waste pipes, she added.