Hassar stream is a watercourse of North East of Casablanca suburban which is a tributary of Mellah river. Until the end of 2012, Hassar stream received wastewater in crude state from Mediouna town causing a degradation of it ecological status and adverse effects on the local population. This work aims to make a first assessment of physicochemical water quality of this watercourse after installing the Mediouna StEp started in 2013. The first results recorded during the first six months of the study (November 2013 to April 2014) shows an improvement in the quality of Hassar stream with dissolved O2 values reaching up to 8,26 mg/l, COD maximum not exceeding 80 mg/l, a maximum BOD5 of 14 mg/l, a maximum content of MES 30 mg/l, ammonium ion (NH4+) in concentrations of 0,9 to 7,8 mg / l, orthophosphates from 0,48 to 11,62 mg/l and nitrates from 4,7 to 25,3 mg/l. These results show that the majority of the stations of the Hassar stream have an average to good quality and the beginning of physicochemical resilience of Hassar stream's waters would be initiated.