Environmental degradation in the middle basin of Conchitas river, Buenos Aires: Two decades of urban and industrial pressure

The Conchitas River, located in the southeastern Buenos Aires Metropolitan Area, has experienced severe degradation due to two decades of unregulated urbanization, industrial effluents, and deficient wastewater management. This study aims to assess long-term changes in water quality in the middle basin of the river from 2002 to 2023. We integrated data from four historical studies with new fieldwork conducted in 2022–2023, evaluating physicochemical, bacteriological, and biological parameters. Results revealed a consistent downstream decline in water quality, with conductivity rising from 629 to 1765 µS cm -1 , dissolved oxygen decreasing from 10.24 to 0.99 mg L -1 , and BOD 5 peaking at 123 mg O 2 L -1 . Fecal coliforms exceeded legal limits across all sites, and diatom assemblages were dominated by highly tolerant taxa. The Water Quality Index (WQI) declined from 67.7 upstream to 37.3 near the mouth. These trends highlight chronic pollution and urgent need for integrated watershed management and investment in sanitation infrastructure.