Surface water is said to be in a good state when its chemical and ecological status is at least good. The physico-chemical quality of water provides only a point-in-time image of the quality of a river. The study of aquatic fauna and flora informs us well of the actual quality of the course of water due to a character integrator of these biological compartments. This makes us to study the quality of the course of the fresh waters of the High Atlas of the region of Marrakech. This study is carried out through various analyses: biotic indices IBGN, IBD, IBGN, BMWP, IPO, IQBR In order to put in evidence the faunistic and floristic particularities of our stations that could structure the state of the hydro-biological quality of the course of waters. The basin of Ourika has hydro geological potential. The study of the hydro-biological quality of the basin slope of Ourika using biological approaches shows heterogeneity in the quality of the water. The quality is good and on average tends toward low. The indices show a net degradation between the upstream and downstream stations, and a variation of the quality of water.

Keywords: Biotic indices, fauna, flora, hydrobiological-quality, freshwater.