Tietê Pollution Patch Shrinks Nearly 16% in 2025, Yet River Remains Vulnerable

Overview

• The SOS Mata Atlântica report measures the pollution patch at 174 km in 2025, down from 207 km in 2024, a 15.9% decrease.
• Only one monitoring site was rated good (1.8%) as most locations remained regular (61.8%), poor (27.3%) or very poor (9.1%), with none classified as excellent.
• The assessment covered 55 sampling points across 41 rivers using the Índice de Qualidade da Água, with data collected by 46 volunteer groups in 24 municipalities.
• Lower rainfall in recent years and episodic pollution events, including a sewage interceptor rupture on Marginal Tietê and illegal discharges in June and August, undermined water quality.
• SOS Mata Atlântica urges revisiting permissive Class 4 water designations and advancing integrated sanitation, land-use measures and nature-based solutions for sustained recovery.