Not far from Latin America’s biggest city, Sao Paulo, a river is covered in a white layer that resembles fresh snow but is in fact a smelly, toxic foam.
The Tiete river, some 1,100 kilometers long, is crucial for potable water, irrigation and energy production in southeast Brazil, the country’s most populated area.
But parts of the waterway, including one area just 100 kilometers (62 miles) from the metropolis, have been befouled by phosphate and phosphorus residues from household detergents used by Sao Paulo’s 22 million inhabitants and washed down the sewers.
In the 1990s, the situation was sometimes so bad that the foam ran down the streets of some cities near the river’s shore.