A section of approximately 100 kilometers along the Tietê River in the interior of São Paulo state has turned green in recent days, a phenomenon believed to be caused by rain and rising temperatures that favor the proliferation of algae. Observations of this green coloration began on Monday, October 16, by residents in municipalities including Adolfo, Buritama, Sales, and Novo Horizonte, with the issue becoming more pronounced by Wednesday, October 18.

In addition to the noticeable color change, residents have reported fish deaths, unpleasant odors, and an increase in water density. These occurrences are attributed to a process known as eutrophication, which is common during this time of year, as consistent rainfall coupled with high temperatures creates ideal conditions for algae growth. The state's environmental agency, Cetesb, has confirmed these observations, pointing out that similar events have occurred in the past in the Tietê River and other water bodies across São Paulo.

This alarming situation raises concerns about water quality and the health of aquatic life in the river. Residents are understandably worried as such environmental changes could have broader implications for local ecosystems and public health. The Tietê River, known for its history of pollution challenges, continues to face significant ecological threats, prompting calls for more stringent environmental monitoring and management.