Residents in the municipality of Adolfo, São Paulo, observed the Rio Tietê displaying a noticeable green color on Monday, October 16. Videos submitted to local news station TV TEM captured the river's murky and dense water. This phenomenon, which has occurred previously, raises concerns about the river's ecological health and impacts on local tourism.

The São Paulo Environmental Company (CETESB) stated that they are actively monitoring the area and noted that the green coloration and the formation of a 'scum' layer are linked to eutrophication. This environmental process is accelerated by recent rains, high temperatures, and increased nutrient concentrations in the water, leading to excessive algae growth and altering the river's color.

The recurrence of such events has implications for the local economy, particularly affecting fishermen and tourism in the area. Earlier in February, residents reported similar issues, highlighting the ongoing environmental challenges facing the region, and underscoring the need for adaptive management strategies to address the health of the river and its ecosystems.