The Seybouse River (Oued Seybouse) is one of the largest rivers in Northeastern Algeria. It rises in the Guelma region and flows through several urban and industrial areas before reaching the Mediterranean Sea near Annaba. Along its course, the river receives domestic, industrial, agricultural, and hospital effluents, which significantly affect its water quality.

This study aimed to evaluate the physicochemical and microbiological quality of the Seybouse River and to assess the extent of pollution caused by human activities. Monthly sampling was conducted over a full year at different stations along the river. The physicochemical analyses included measurements of temperature, pH, electrical conductivity, major cations (Ca²⁺, Mg²⁺, K⁺, Na⁺), anions (Cl⁻, SO₄²⁻, NO₃⁻, NO₂⁻, NH₄⁺, HCO₃⁻), and organic pollution indicators such as BOD₅, COD, and suspended solids.

The microbiological assessment focused on fecal contamination, pathogenic bacteria, and yeasts, summarized through a microbiological contamination index.

Results showed clear spatial and temporal variations, identifying high mineral, organic, and fecal loads, especially downstream. These findings reveal that the Seybouse River is heavily polluted and that its water presents serious environmental and health risks, making it unsuitable for irrigation or any direct use.

The spatiotemporal variations of many physicochemical and microbiological parameters indicated intensive pollution of the Seybouse River. This pollution was reflected by a significant mineral, organic and faecal load downstream of the river. Our study indicates that the water of the Seybouse River is highly degraded and presents a real threat to aquatic life. The Seybouse River is heavily polluted, and its water presents serious environmental and health risks. Our study also suggests that the use of river water for crop irrigation should be avoided.