In this study, the water quality data obtained from 6 sampling stations between July 2011 and June 2012monitoring period at Mert stream was evaluated. In order to assess the present water quality of Mert stream, differentWQI approach (modified WQImin) was applied to a data set expressly collected for the present study. The mean WQIvalue of the stream is 81.9, which lies on the mid water classification region, so the water is considered at fair quality.The resulted WQI shows that 91.6, 92.5, 74.3, 91.6, 75.2 and 62.5 for sites St1, St2, St3, St4, St5 and St6 respectively.Among stations, there was significant variations in water quality index from poor quality to good quality that St5 and St6in urban part and St3 in rural part of the stream are under the pressure of pollution. While the reason of the low waterquality in 5th and 6th stations is based on domestic and industrial wastes, the reason of poorness in 3th station arises frompoultry farm wastes poured intensely from chicken farms near the station into the stream in Kavak district. The mosteffective water quality parameters are pH, electrical conductivity (EC) and total suspended solids (TSS) on thedetermination of WQI for the present study.