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White foam on the Tietê River has once again drawn attention in Salto, in the interior of São Paulo, amidst rains, increased flow, accumulated pollution, and new sanitation actions that attempt to reduce the historical impacts on water quality.
A white and dense layer once again covered part of the Tietê River in Salto, in the interior of São Paulo, on Thursday afternoon (25), drawing the attention of residents and reinforcing the alert about pollution in the area.
According to the Environmental Company of the State of São Paulo (Cetesb), the phenomenon is linked to the increase in the river’s flow during the rainy season, combined with the presence of a pollutant load in the water.
Cetesb’s explanation indicates that the foam does not arise from a single isolated factor, as the increase in water volume intensifies the river’s movement and favors the formation of the visible layer on the surface.
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In areas of greater turbulence, residues and pollutants present in the watercourse tend to mix more intensely, which helps explain why the foam appears so prominently in certain spots.
Foam on the Tietê River in Salto
Commenting on the case, the president of Cetesb, Thomaz Toledo, stated that the occurrence becomes more noticeable when there is an increase in the flow of the Tietê River, especially during rainy periods in the region.
“This happens mainly at the headwaters of the Tietê River, when the increase in the river’s flow increases the water volume and foam production,” he said.
Although the rains help explain the strength of the phenomenon, the presence of the foam also exposes the pollution load that still reaches the river, a problem directly related to basic sanitation.
Toledo highlighted that improving water quality depends on expanding sewage collection and treatment, as these pollutants remain among the main factors of the Tietê’s degradation.
“Since we have a significant pollution load, it is very important that investments in sanitation occur,” stated the president of Cetesb.
In the same statement, he reinforced that “there is no other way” to improve the river’s quality without expanding this type of investment.
In Salto, the foam tends to gain attention because it appears in large volumes, changes the river’s landscape, and makes visible an environmental problem that remains associated with urban occupation and the discharge of pollutants.
The episode, however, is part of a broader discussion about sewage collection and treatment in the Tietê basin, which crosses densely urbanized areas and receives direct impact from the São Paulo Metropolitan Region.
Sanitation and Recovery of the Tietê
To tackle this scenario, the São Paulo Government maintains the IntegraTietê program as one of the main initiatives to expand sewage collection and treatment, recover degraded areas, and improve water quality.
The initiative brings together works executed by Sabesp and actions coordinated by the Department of Environment, Infrastructure, and Logistics, focusing on municipalities in the São Paulo Metropolitan Region and Alto Tietê.
According to Semil, since 2023 Sabesp has connected more than 1.1 million households to the sewage network, as part of the set of actions planned for the recovery of the basin.
The program’s goal is to reach 1.5 million new connections by 2026 and more than 2.2 million by 2029, expanding the necessary infrastructure to reduce sewage discharge into the rivers.
This expansion is considered essential because foam formation is associated with the combination of flow, water agitation, and the presence of pollutants, especially in sections where the river suffers greater urban impact.
With more sewage collected and treated before reaching the watercourses, the trend is to reduce the organic load discharged into the water system, although the results depend on continuous execution, inspection, and monitoring.
In 2026, Cetesb reported a 20% reduction in organic load in the Tietê, according to a statement attributed to the company’s president, who linked the progress to sanitation actions and environmental monitoring.
Thomaz Toledo stated that, with these numbers, it will be possible to tackle the foam problem in the Salto region, in conjunction with state actions aimed at inspection and monitoring of water quality.
Water Quality Monitoring
In addition to sanitation works, Cetesb expanded the monitoring network of the Tietê River to more accurately measure changes in water quality along the basin.
In April 2024, the company reported that the measurement points increased from 11 to 30, within IntegraTietê, and adopted Total Organic Carbon as an indicator to monitor the organic load.
According to the Semil, the new indicator takes into account the average daily flow and the concentration measured at the time of collection, allowing for tracking variations that can directly interfere with the river’s assessment.
In 2023, the measurement took place on two fronts: the organic load generated in the Alto Tietê basin and the average concentration in the river’s tributaries located in the same region.
The department reported that the first results of the new model showed improvement above expectations in 12 months, with an average annual load of 202 tons per day, below the target of 210 tons per day.
In the same survey, the weighted average of total organic carbon was 30.6 mg/L, an index lower than the expected limit of 34 mg/L for the monitored period.
In parallel, the company maintains automatic stations at strategic points, such as Mogi das Cruzes, Pirapora-Rasgão, Itu, and Laranjal Paulista, to monitor water parameters more frequently.
These devices record dissolved oxygen, pH, turbidity, electrical conductivity, and temperature at five-minute intervals, providing data that help interpret changes caused by rain, flow, and pollution.
As the behavior of a river is directly influenced by climatic factors, assessments of water improvement or deterioration need to consider averages, seasonality of rains, and flow variations, not just isolated episodes.
In the Salto section, the foam once again served as a visible sign of an old problem, while the reduction of organic load and the expansion of sanitation indicate gradual progress in the recovery of the Tietê.
Even so, the recurring presence of the white layer shows that improving water quality depends on the continuation of works, environmental monitoring, and permanent monitoring throughout the basin.
