The Algerian west coast is the prime recipient of several forms of pollution; hence, the necessity for an impact assessment of this coastal pollution using a suite of recommended marine biomarkers, including lysosomal membrane stability in living cells by the Neutral Red Retention Time (NRRT) method, the evaluation of micronucleus (MN) frequency, and the determination of acetylcholinesterase (AChE) activity in mussels Mytilus galloprovincialis, sampled from the large, polluted Oran Harbour (OH) and the Maârouf (Mrf) marine mussel farm between July 2005 and April 2006. The difference in the variations of the annual physical parameters between OH and Mrf corresponds to the influence of the domestic and industrial sewage discharged by the city of Oran. The biological data of the mussels (condition index, protein content) recorded at both sites were related to their natural reproductive cycle. This indicated that intrinsic variation between the sites due to different mussel development phases was minimal. The variation in the AChE activity of some organs of OH and Mrf mussels, with minimal inhibition in July and a higher NRRT recorded in the granular haemocytes in the Mrf than in the OH mussels during the autumn and spring, depends on the quality of the biotope and on generic stress factors. Moreover, the variation in MN frequency, in general reflecting a non-significant seasonal and spatial genotoxic effect of the contamination at the two sampling sites, requires further investigations regarding biotic and abiotic variations.