Pollution in the stretch of the Rio Tietê passing through Greater São Paulo recorded a reduction in 2026, according to a study published this Thursday (17) by Cetesb (São Paulo State Environmental Company), an agency linked to the state government.
The average organic matter transported daily by the river fell from 210 tonnes in 2025 to 154 tonnes this year, a reduction of 26.7%, according to the survey. In 2024, the figure was 218 tonnes per day.
Measurements are taken at the dam of the Small Hydroelectric Power Plant (PCH) Edgard de Souza, located in Santana da Parnaíba, at a monitoring point at the exit of the metropolitan region of the state capital.
This point makes it possible to track the amount of organic matter carried by the Tietê after the river passes through the most urbanised area of the state and heads toward the interior. For the 2026 average, the study took into account the flow from the first two quarters.
In calculating the pollution load, Cetesb considers both the concentration of organic matter and the volume of water flowing in the river. This makes it possible to determine how many tonnes are transported per day and to compare rainy and dry periods.
Waste reaches rivers mainly through the discharge of untreated domestic sewage. This reduces the oxygen available in the water, generates a strong odour, harms aquatic life and contributes to the deterioration of river quality.
The Secretary of Environment, Infrastructure and Logistics of the Tarcísio de Freitas (Republicanos) government, Natália Rezende, attributes the improvement to investments made in basic sanitation, planning and a diagnostic assessment of the condition of each sub-basin of the state's rivers.
According to her, the privatisation of Sabesp played a fundamental role in improving actions against pollution.
"Guarulhos in 2019 treated 1% of sewage. Cajamar, Franco da Rocha and Francisco Morato were at 0% in 2022. Salesópolis, for example, where the Tietê originates, had 4,300 households under the old Sabesp contract, but another 1,800 were outside it," she said.
Rezende said she believes the state will be able to achieve universal sanitation coverage before the 2033 target.
"When we planned the [state programme] Integra Tietê in 2023, we looked at the river's 1,136 km. To, in an organised way, create action areas and tackle each of the challenges. The first area focused on health and quality of life, linked to sewage disposal. The second focuses on dredging," she said.
More than 6.5 million cubic metres of sediment have been removed since 2023, the secretariat states. In 2025, more than 2.3 million cubic metres of sediment were removed from the Tietê and Pinheiros rivers, the equivalent of 192,000 full lorry loads.
The removal of floating waste — including plastic, furniture and other debris — is also part of the secretariat's restoration efforts. On the Pinheiros, 147,000 tonnes of such materials have been removed since 2023.
Malu Ribeiro, director of public policy at SOS Mata Atlântica, says that despite the reduction, the load remains high. The NGO also conducts annual studies on the Tietê, which point to a worsening trend. In her view, the river accumulates not only domestic sewage but also industrial waste and litter carried by rainfall.
"With each passing decade, in which we wait for the Tietê's clean-up and fight for it, the challenges grow, because extreme weather events arrive along with new sources of pollution, such as pharmaceutical products, microplastics and a range of other pollutants," she stressed.
