‘Good lord, what a smell’: can Brazil’s biggest city save a vital source of water from sewage, bacteria and organised crime?

As São Paulo faces a climate-induced water crisis, campaigners are fighting to reverse the impact of pollution and illegal deforestation on its largest reservoir

In a small motorboat laden with water-monitoring equipment, biologist Marta Marcondes and community activist Wesley Silvestre Rosa cross Billings reservoir on the far southern edge of São Paulo. Bright white herons glide over the water, which is flanked by thick dark green clusters of Brazil’s Atlantic forest, as the boat heads towards one of the more polluted parts of the reservoir.

“We see where sewage is entering, we see what has been deforested and how that has affected the water quality of the reservoir,” Marcondes says.