The quality of Wady Eqab waste water which is considered one of the major sources of Tigris river pollution in the north Mosul city have been investigated , physical , chemical and bacteriological tests of water samples which were taken from different sites of the Wady Eqab have been conducted to know the degree of pollution and the effect of this sewage on the water quality of the Tigris river. The results indicated significant reduction in dissolved oxygen concentrations in the water with the high values of organic load, Sulfate, Chloride, total number of bacteria , fecal coliform and E. coli. Their rates 53.6 mg / l ,153.1mg /l, 2.26 mg/l 123.2 × 106 cells / 1 ml and 255.6, 255.6 × 106 cells / 100 ml respectively, same indication was noticed for most investigated parameters ,whereas a great reduction in some of the parameters of pollution was recorded at the end of Wady Eqab, such as organic load and the indicators of bacterial contamination due to the self-purification and the synergistic effect of the water temperature and solar radiation, A significant effect of Wady Eqab water on Tigris River water was noticed at cite 6 which is located 500 meter below the confluent of wady with the river and the effect extended up to 200 meters.