The Bahía Blanca Estuary, located at the Atlantic coast of Argentina, includes a governmental nature reserve to protect biodiversity, lands and water; however, as the process of industrialization and urbanization is stepping rapidly at the neighbouring area, the potential increase in contaminant loads is a serious concern. After several contaminants surveys at the estuary, no single study has been yet performed in order to study the native mussels population assemblages vs. the chemical environment; then, to test the ability of Brachidontes rodriguezii assemblages as pollution indicators, native populations were chosen at three different sites from the Bahía Blanca Estuary.