The Nonhon and Gninhn rivers, in the west of Côte d’Ivoire, are under considerable pressure due to mining and agricultural activities carried out around them. This study therefore aims to know the composition, structure and dynamics of microalgae in said rivers. Thus, the micro-algal flora and the physicochemical parameters of these rivers were sampled every 45 days from 9 a.m. to 2 p.m. from October 2020 to February 2022. In total 103 taxa distributed between 30 genera, 20 families, 15 orders, 4 classes and 4 phyla were collected, of which the Euglenophyta phylum is more diverse. The Gninhin river records 100 taxa and that of Nonhon mentions 97 taxa. Abundance and species diversity are high in the two rivers during the main rainy and dry seasons in the Nonhon and Gninhin rivers respectively. Bacillariophyta dominate the micro-algal population whatever the river. The spatial-seasonal dynamics of microalgae revealed significant variations, with a peak in abundance during the long rainy season and the long dry season respectively in the Nonhon and Gninhin rivers. The spatio-seasonal results of chlorophyll a indicate a proliferation of microalgae during the rainy season compared to the dry season. The dynamics of microalgae from the Nonhon and Gninhin rivers evolve over time and depending on the stations.
