Many researchers become attracted to biological and ecological studies in water resource management. These studies mainly focused on identify and describe the characteristics of the ecosystem, living organisms and environmental factors. Water quality evaluation of drinkable water is highly essentialdue to the reduction of its quality and quantity in urban area. Water quality indices can be used as a decision support tool to assess water quality without using complicated mathematical and statistical analysis. Zayande-rood's dam lake is the most important water supply of drinking, industrial and agricultural sectionsin Isfahan and Yazd province. The Zayande-rood's dam lake is located in longitude, 50°, 44', 18" and 50°, 36', 4"east and latitude 32°, 43', 34" and 32°,43', 5" north, 110 kilometers of west Isfahan. Five sampling points in the dam lake were selected to assess water quality based on the previous studies. Sevenwater samples were collected every 45 days from all the sampling points (two samples in each season) from May 2013 to March 2014. The water quality parameters of the collected samples were measured including DO, NO 3 , NO 2 , NH 4 , PO 4 , hardness, pH, EC, TDS, TSS, TS, COD, BOD 5 .Water quality indexes were then calculated and compared with international standards accordingly. According to the calculated WQI index scores (50-100), Zayande-rood's dam lakehad good water quality butthe NSFWQI a and NSFWQI m indexes categorized dam lakewater quality in mid- Key words: Water quality index, physicochemicalparameters, Zayande-rood dam, Isfahan, WQI, NSFWQI
