The aim of the present study is the rst to evaluate the ecotoxic state of the marine environment in Anza-Taghazout coasts (Morocco) after installation of two Wastewater Treatment Plants using a natural population of marine bivalves M. galloprovincialis. These coasts are exposed to many discharges generating, thus, different sources of pollutants. These pollutants can modulate the physiological responses of marine bivalves to environmental stress. In this context, a multi-biomarker approach consisting of a battery of biomarkers evaluation was used to assess the response of these species to stress. In the whole soft tissues of M. galloprovincialis, four biomarkers were evaluated: Acetylcholinesterase (AChE), Glutathione S-transferase (GST), Catalase (Cat) and malondialdehyde activity (MDA). In parallel, physico-chemical parameters were measured in the marine water of Anza-Taghazout within three selected sites: S 1 considered as 'hotspot' located at Anza city; S 2 located near of Aourir city and the third site, S 3 'reference' located in Imouran beach. Our results showed that activities of both Gluthation-S-Transferase and Catalase were higher in M. galloprovincialis collected from site S 1 , but high values of Malondialdehyde and Acetylcholinesterase activities were observed successively at S 3 and S 2 . Application of Integrated Biomarker Response index (IBR) was suitable for classifying the stress response in the M. galloprovincialis but did not allow to evaluate the level of the xenobiotic exposure in the studied sites. The statistical results did not show any signi cant differences between the three studied sites and therefore S 1 has recently become clean due to the installation of two wastewater treatment plants.