Context: The high population density and the increase in agro-industrial activities, which characterize the south of Côte d'Ivoire, are increasingly contributing to the degradation of aquatic ecosystems. This unfortunately leads to the destruction of natural habitats of aquatic species, especially through the action of an agriculture that constantly uses agricultural inputs (fertilizers, pesticides, etc.). Objective: This study aims to analyze the impact of human activities on surface water pollution, with a view to possibly alerting public opinion and decision-makers. Methodology: The methodology adopted is that of using micro-algae as bio-indicators of harmful actions due to man on surface waters. Water samples were taken from two rivers in the south of Côte d'Ivoire, one with low activity (la Mé) and the other with high activity (le Boubo). After the identification and enumeration of microscopic algae, the floristic richness and density of microalgae were analyzed. Results: The results obtained showed that in terms of floristic richness, the Boubo River provided 65.70% of the total tax collected, compared to 34.30% for the Mé River. Similarly, the spatial-seasonal analysis of phytoplankton density indicates that the Boubo is denser (89.76%) than the Mé (10.24%). Conclusion: This study, which is the first of its kind to be carried out on the Boubo and Mé rivers, will therefore serve as a basis for comparison for further research, but above all as a means of alerting to the harmful actions of man on aquatic ecosystems.