Anthropogenic activities have led to water quality deterioration in many parts of the word, especially in Northwest Algeria. The current work investigated the spatiotemporal variations of water quality in the Cheliff River, samples for physico-chemical were performed at different periods from 2004 to 2007, the results chowed that nitrate (NO3-)  intake is very high especially in the month of February 2006 (26 mg/l) and February 2007 (37 mg/l), nitrite (NO2-) values also exceed the standard for samples taken at the estuary (and the sea), ie 0.96 mg/l in the month of February 2006 and 0.98 mg/l in April 2007;the Ammonium (NH4+) contributions are due to the River because the value recorded at the estuary (4.22 in February 2006) ;silicate (SiO2) varies greatly depending on the River flow resulting from soil leaching SOUR to the estuary where we see the maximum values of  20.10 mg/l in the month of February 2007 and 19.1 mg/l in March 2005. The recorded values of elements phosphorus (PO4---) are high and very variable from 0.01 to 1.90 mg/l for the River, 0.01- 0.80 mg/l for the estuary and 0- 0.49 mg/l for the sea. The analyzed biological confirmed a total of 41 phytoplankton speciesand31 macroalgae species. So, Aquatic ecosystems are particulury vulnerable to environmental change and many are, at present, severely degraded.