The objective of the study is to assess the ecological quality of the river Lobo and its two main tributaries. To do this, spatio-seasonal measurements of physical, chemical and biological parameters were carried out in situ using a multiparameter and by assay in the laboratory. No significant variations were observed across the physicochemical parameters with the exception of orthophosphate at a spatial level. The concentration of chlorophyll a ranged from 57.67 µg/L to 149.91 µg/L while that of total phosphorus ranged from 5.58 mg/L to 25.85 mg/L at the river Lobo. These values fall within the range of values for the eutrophic state. Regarding organic pollution, the index values range from 2.47 to 3.13 indicating a moderate level of organic pollution in the river Goré, from moderate to high in the Lobo River, and a high level of organic pollution in the river Dé. Additionally, the Carlson trophic index suggests that the rivers are eutrophic. From the above results, it can be seen that the river Lobo and its main tributaries are impacted by organic pollution with enrichment in nutritive salts linked to the anthropic activities carried out in the basin. The waters in the upstream of the basin are more affected by human activities than those in the downstream.