Coastal ecosystems receiving untreated industrial effluents are increasingly exposed to microbiological and organic pollution. This study evaluated the impact of wastewater discharges from fish-processing industries on the seawater quality of Lévrier Bay (northwestern Mauritania). Two sampling campaigns were conducted during the cold and warm seasons at six stations located within the seawater–wastewater mixing zone. Microbiological indicators (total coliforms, Escherichia coli, and fecal streptococci), physicochemical parameters (temperature, pH, salinity, electrical conductivity, total dissolved solids, and dissolved oxygen), nutrients (nitrate, nitrite, and phosphate), and organic pollution indicators (BOD5) were analyzed. Microbiological results revealed severe fecal contamination, with total coliforms reaching 8.8 x 105 CFU/100 mL, E. coli up to 8.5 x 105 CFU/100 mL, and fecal streptococci up to 8.1 x 105 CFU/100 mL. Physicochemical conditions generally remained within natural coastal ranges, with pH (7.53 - 8.5), salinity (30.43 - 35.08 PSU), and temperature (21.71 - 25.83 °C). However, elevated BOD₅ (up to 225 mg/L), phosphate (2.4 mg/L), and low dissolved oxygen (1.78 mg/L) indicated localized organic enrichment and potential hypoxic conditions. Overall, the results demonstrate that untreated industrial discharges from fish-processing industries exert significant microbiological and organic pressure on Lévrier Bay, highlighting the urgent need for wastewater treatment and continuous environmental monitoring to protect this vulnerable coastal ecosystem.