ABSTRACT
Nahr el Bared is one of the main Lebanese coastal rivers. It crosses down a rather deep valley and passes by several urban agglomerations and industrial zones, which use its water as a discharge system of their waste. This study shows the impact of the anthropic activities on the water quality of this river. The application of the diversity and the similarity index, and the biological normalized index IBGN, as well as the statistical analyses of correlation permit to characterize a sector close to the source free of pollution whereas most of the course downstream is subjected to strong anthropic disturbances which degrade the quality of water to more or less high intensities according to the inputs and the self-purification. A positive correlation of the chemical, biological and bacteriological pollution indicators is highlighted