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Foam formed by pollution and sewage once again takes over the Tietê River in Salto, in the interior of São Paulo, in an annual phenomenon that exposes the environmental collapse of São Paulo’s most important river and puts residents and tourists at risk
A dense layer of toxic foam once again covered the Tietê River in Salto, in the interior of São Paulo, this Thursday (14). According to g1, the phenomenon, which repeats every year, is caused by pollution and untreated sewage dumped in Greater São Paulo and carried downstream to the city’s waterfalls, where chemical residues are agitated and form the white foam that has taken over the landscape.
Aerial images captured the Tietê River completely covered by foam near the Tourist Complex of the Waterfall. According to the SOS Mata Atlântica Foundation, the Tietê River receives about 600 tons of garbage and pollutants per day. The scene, which should cause outrage, has become routine, and both the City Hall of Salto and the Environmental Company of the State of São Paulo (Cetesb) monitor the situation while warning that contact with the foam can cause skin and eye irritation.
Why toxic foam forms in the Tietê River in Salto
The foam that covers the Tietê River is not a natural phenomenon. It arises when residues from detergents, chemicals, and other substances present in domestic and industrial sewage are dumped untreated into the river. Along the route between Greater São Paulo and the interior, these compounds accumulate in the water. When the flow of the Tietê River meets the waterfalls in Salto, the mechanical agitation transforms the pollutants into a mass of foam that spreads for hundreds of meters.
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Cetesb attributed this week’s episode to the rain recorded last Sunday (10), which would have “washed” pollutants accumulated on the banks and in smaller tributaries, bringing all this load of pollution to the main bed of the Tietê River. The combination of dry periods, which concentrate the sewage, and occasional rains, which drag everything at once, creates the perfect scenario for foam formation in proportions that shock those who see it for the first time and discourage those already familiar with the long-standing problem.
600 tons of pollution per day: the numbers that explain the collapse of the Tietê River
Data from the SOS Mata Atlântica Foundation reveal the extent of the problem. The Tietê River receives about 600 tons of garbage and pollutants daily, a volume equivalent to the weight of more than 400 compact cars dumped in the water every 24 hours. Most of this load comes from the domestic sewage of the São Paulo Metropolitan Region, where millions of inhabitants still lack adequate effluent treatment.
The pollution of the Tietê River is not limited to residential sewage. The discharge of industrial effluents, irregular disposal of solid waste, and unregulated occupation of the banks contribute to a degradation scenario that has persisted for decades. Recent analyses detected concerning chemical compounds and indicated an increase in pollution in sections of the Tietê River in the interior of São Paulo, showing that the problem is not confined to the capital and spreads throughout the watercourse, even reaching regions far from Salto.
Salto between tourism and risk: the foam that attracts and threatens
The city of Salto maintains a contradictory relationship with the Tietê River. The Waterfall Tourist Complex is one of the main visitation points of the municipality, and the foam itself, as toxic as it is, ends up attracting curious people who want to capture the phenomenon up close. The Civil Defense and the City Hall of Salto warn that this proximity poses a real health risk, potentially causing skin and eye irritation.
In an official statement, the City Hall of Salto stated that the problem is recurring and that the solution depends on ending the discharge of untreated sewage into the Tietê River. “Every year this phenomenon happens here in Salto and would only end if the cities of Greater São Paulo ceased the discharge of pollution,” says the statement. The declaration highlights a stalemate that repeats as much as the foam itself: the municipality that suffers the most dramatic visual and environmental consequences is not the one that generates most of the pollution, and the responsibility falls on dozens of municipalities and the state government.
Cetesb intensifies inspection, but sewage continues to reach the Tietê River
Cetesb highlighted that it maintains continuous monitoring work in the Tietê River region and that, since March 2025, it has conducted 419 inspections in the area. The significant number of inspections, however, did not prevent the foam from re-forming, which raises questions about the effectiveness of control actions while the source of the problem remains unchanged: the massive discharge of sewage and pollution occurring upstream.
The challenge is structural. As long as the sewage collection and treatment system of Greater São Paulo does not achieve full coverage, the Tietê River will continue to function as a waste transport channel. Each inspection and each fine imposed by Cetesb addresses symptoms of a problem whose cure requires billion-dollar investments in basic sanitation, infrastructure that advances at a slow pace in the face of the environmental urgency that the toxic foam in Salto makes impossible to ignore.
From excess rain to foam: the Tietê River between two extremes
The episode of toxic foam in Salto occurs a few months after the Tietê River experienced a major flood in February of this year. On that occasion, the flow reached 520 cubic meters per second, well above the normal average of 200 to 300 cubic meters per second. According to the National Center for Monitoring and Alerts of Natural Disasters (Cemaden), the main factor of the flood was not local rain, but the enormous volume of water coming from the Metropolitan Region of São Paulo, which flowed down the river course and reached interior cities with force, including Salto.
This alternation between extreme floods and episodes of toxic foam reveals that the Tietê River suffers in both scenarios. With heavy rain, water contaminated by sewage and pollution overflows and causes floods. With little rain, the concentration of pollutants increases and any isolated precipitation drags the accumulated load to the waterfalls, generating foam. The river functions as a thermometer of the sanitary failure of the largest metropolis in South America, and what is seen in Salto is just the most visible manifestation of a crisis that runs throughout its course.
The future of the Tietê River depends on decisions that no one wants to make
The Tietê River does not need more diagnoses. The data is available, the 600 daily tons of pollution are known, the source of untreated sewage is mapped, and the foam in Salto appears punctually every year as a visual reminder of the problem. What is lacking is political will and continuous investment in basic sanitation in Greater São Paulo, actions that would benefit not only the river but millions of people who live daily with the effects of pollution in their homes, neighborhoods, and water bodies.
Meanwhile, the Rio Tietê continues carrying the sewage of an entire metropolis and depositing the result in the waterfalls of Salto, in the form of a white and toxic foam that no resident of the region should be forced to accept as normal. The question that arises is how long the largest river in the state of São Paulo will be treated as an open-air sewage channel.
And you, what do you think about this situation? Do you believe that the Rio Tietê can still be recovered, or have pollution and untreated sewage already condemned the river irreversibly? Leave your opinion in the comments.
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