Rio Tietê remains vulnerable despite the 15.9% reduction in the pollution stain

O It remains vulnerable, despite the 15.9% reduction in its pollution stain -improper water extension for multiple uses -from 207 kilometers (km) by 2024 to 174 km by 2025. Only one point analyzed by the SOS Mata Foundation throughout the Tietê basin presented good condition water. Considering the collections made this year, most remain regular, bad or terrible. The conclusion is from the most recent edition of the study watching Tietê, launched on the eve of Tietê River Day, on September 22, the largest Rio Paulista. With 1.1 thousand kilometers from the source to the mouth, the tietê crosses the state of from east to west and cuts urban, industrial areas, hydroelectric power generation and agricultural production.

“Analyzing the results obtained in this report, we can see that there is still great stagnation in relation to the improvement of the water quality of our rivers. We had no major improvements except the reduction of pollution spot compared to last year, but is still larger than in previous years,” said Gustavo Veronesi, project coordinator observing the rivers in the SOS Atlantic Forest. Based on the number of monitored points throughout the Tietê basin, those classified as good quality represent 1.8%of the total, while most remained among regular (61.8%), bad (27.3%) or terrible (9.1%) categories. Once again, there were no points classified as great.

In total, 55 points were analyzed in 41 rivers of the Tietê Basin, based on the water quality index (IQA) – an indicator that considers physical, chemical and biological parameters (such as dissolved oxygen, fecal coliforms, turbidity, phosphate, nitrate), and classifies water into five categories (great, regular, bad or bad). The Tietê Basin covers 265 municipalities, in a total of more than 9 million hectares – 79% inserted in the biome

The data, according to SOS Mata Atlântica, reveal that the basin lived a recovery cycle between 2016 and 2021, when the regular and good water quality increased and the pollution stain, which is specifically measured on the Tietê River, reached the smallest recent level, with 85 km. From 2022, however, this positive trajectory was reversed, as the stain grew again, reaching the 207 km peak in 2024, while the stretches of good water in the basin diminished. “When we look at the historical series, we realized that the worsening in 2024 was not an isolated point, but the aggravation of a setback trend started in 2022. Despite annual fluctuations, the quality of the tietê remains highly vulnerable and there are no consistent signs of lasting recovery,” said Veronesi.

Loss of good water

Significant loss of good quality water along the river is a matter of concern. In the stretch of Tietê between the source, in Salesópolis, and Barra Bonita – which corresponds to the first 576 km of the river – the report points out that 120 km had poor quality (against 131 km in 2024) and another 54 km were classified as terrible (76 km the previous year). However, good quality water was restricted to only 34 km, between Salesópolis and Biritiba Mirim, a reduction of over 70% over the 119 km recorded in 2024. The regular condition advanced to 368 km compared to 250 km last year.

The evaluation of the SOS Atlantic Forest is that, although the predominance of the regular condition represents a breakthrough in relation to previous scenarios, this classification still imposes restrictions on the multiple uses of water and highlights the high vulnerability of the river. According to Veronesi, quality remains highly susceptible to climate variations, discharges and remnants of treated and untreated sewage, dam operations, extreme event effects and environmental accidents, which reinforces the need for continuous surveillance and the urgency of structural depollution actions.

The expert says that the vulnerability of the river is evidenced by additional pressures, such as the significant reduction of rainfall in recent years (from 2,050 mm in 2010 to 1,072 mm in 2024), which compromises pollutant dilution. In addition, incidents such as the rupture of a sewage interceptor at Marginal Tietê in July and irregular evictions on the Pinheiros River and Tietê himself in June and August contributed to nullifying part of recent advances. “Indeed, it is very difficult to achieve good quality, because it is much easier to pollute a river than to disrupt. It is a gigantic effort, it does not depend on one or another, it depends on an effort of society, the community, and it is obvious that some parts have greater responsibilities, especially public, state and municipal powers, and also companies, which also have huge responsibility in this process of depollution,” he said.

According to him, one of the factors that impact river pollution is the incorrectly discarded garbage, which ends up to Tietê. “This has a relationship [com as empresas]because we have in the Solid Waste Law on reverse logistics, but it is not applied in practice. So, companies end up not being responsible for the packaging that generates [essa poluição].”

Depollution actions

“The continuity of Tietê’s depollution works is critical for reducing the stain, and this needs to be constant. We hope that the works will continue so that we can, next year, give more news of reduction, because it needs to be a process, never eventually be careful with basic sanitation, mainly in the Alto Tietê basin, which corresponds to the Metropolitan Region, with the largest cluster. Urban of South America, ”he said. He points out that a very large portion of this population is not met by the basic sanitation service and that many even have no access to decent housing.

“We need to have social justice, an improvement in the quality of dwellings, more dignified housing for people, so that they are linked to the sewage system. You can’t charge people to be linked to the sewage, if you don’t even live, they often have.” Rivers depollution, however, not only depends on sewage treatment, Veronesi recalled. He also cited the need for solid waste management, the best use and occupation of the basins in the basins that Tietê passes, construction of more linear parks in the rivers, protection of springs, and advancement in basic sanitation.

The Tietê River has different water framing classifications, which vary according to the preponderant uses in each of its watershed. Defined by law, the classification varies from the special class to class 4, the latter the most permissive in relation to the receipt of pollutants. In the Alto Tietê, the spring areas are framed in class 1, while most of the rivers and urban streams, such as Tamanduaateí, Pinheiros and Tietê itself, in the stretch of Pirapora do Bom Jesus is in class 4. Veronesi points out that some excerpts remain poor quality, even after decades of investments in recovery. He evaluates that to recover the rivers of the basin, the maintenance of class 4 as a reference needs to be reviewed.

*With information from Agência Brasil