Abstract: Background and Objective: Untreated municipal sewage, garbage and industrial effluents are directly or indirectly discharged into the lagoon and are the contributing factors of its degradation. Many water quality studies conducted in Cote d'Ivoire revealed that this problem contributes to the pollution of water resources. This study aims to evaluate the physico-chemical parameters and algal variation in the bay of Bietry in the neighborhood of Port-Bouet slaughterhouse in order to appreciate the impact of its effluents on this bay. Materials and Methods: Sampling was carried out in the South of Bietry bay towards the slaughterhouse during the dry season and the wet season. Water samples were collected at 10 stations for biological oxygen demand (BOD5), chemical oxygen demand (COD), total suspended solids (TSS), pH, temperature, salinity, redox potential and chlorophyll analyses. Variation of each parameter between sites and seasons was analyzed statistically through the test of Mann-Whitney at 5% level of significance. Results: It was found that, the COD (1988.50-10965.00 mg L–1), BOD5 (612.50-3813.50 mg L–1) and TSS (195.00-285.00 mg L–1) concentrations, as well as temperature (23.20-32.40°C), pH (7.65-9.01) and salinity (16.40-23.90) values were higher during the dry season than the values of wet season. On the contrary, during the dry season, chlorophyll values (0.65-13.25 mg L–1) were lower than the values (8.94-41.3 mg L–1) of wet season. Conclusion: The study revealed that the pollution of Bietry bay is controlled by its exchange with the ocean, freshwater inputs and rainfall. Thus, the dilution during the raining season by oceanic water and the rain reduces considerably the concentrations of pollutants and increases salinity and algal production.