Lebanon is a mountainous country with an area of 10452 km2, and it is characterized by a Mediterranean climate having a variable rainfall rate from which a significant amount is manifested as snow. The dense population of Lebanese is located in the coastal zone creating a strong anthropic pressure on the water resources. The civil war (1975-1990) and the post-war period (1990-2000) have led to a shortage in Lebanese watersheds data due to discontinuation of regular measurements. This study aims at investigating the hydrological response of the Al-Zahrani River Basin by tackling various physicochemical and microbiological parameters that are related to human activities’ influence on the water quality in six selection sites. The water tested physiochemical parameters of the basic temperature (T), the potential of hydrogen (pH), electrical conductivity (EC) and total dissolved solids (TDS), the anions (NO3 - , SO4 2- and PO4 3-), the cations (Na+ , K+ , Ca2+, and Mg2+), and the heavy metals (Cd, Cr, Fe, Cu and Zn). The microbial parameters are Salmonella, Escherichia coli, Total Coliforms, Clostridium perfringens and Staphylococcus aureus. Furthermore, the most polluted site was assessed through conduction of principal component analysis (PCA) statistics. Microbiological pollution was found at a high level in all sites with a total absence of heavy metals contamination. High nitrate levels were observable in two sites (WadiAkhdar 2 and Zahrani), in addition to a high potassium rate in NabehKfarwah. The PCA assessment highlighted the Zahrani site as the most polluted. The main pollution causes are correlated with wastewater discharges and industrial activities.