In northern Côte d’Ivoire, water reservoirs are subject to increasing anthropogenic pressure due to the intensification of agricultural and pastoral activities. This study aims to analyze the seasonal dynamics of eutrophication in the waters of Lake Nafoun, located in the Poro region. The methodology consisted of water sampling during two campaigns: one during the dry season (April 2025) and another during the rainy season (September 2025), followed by physicochemical analyses in the laboratory. The results show that nutrient concentrations (NO2⁻, NO3⁻, NH4⁺, total nitrogen, total phosphorus, and PO43⁻) are significantly higher during the dry season than during the rainy season. Chlorophyll a content exhibits a similar trend. According to the OECD (1982) classification, the trophic state during the dry season ranges from eutrophic to hyper-eutrophic, while during the rainy season, it ranges from mesotrophic to hyper-eutrophic. These findings highlight the determining influence of seasonal variations on the degree of eutrophication of Lake Nafoun and underscore the need for integrated water resource management strategies in the Sahelian-Sudanian zones of West Africa.