Population growth, industrial development, climate changes and environmental pollutants reduce the quality of available water resources. Nowadays, limited resources of freshwater and maintaining their qualities are the biggest challenges for the management of water resources. To investigate the water quality of Tajan River, 4 sampling stations were selected along the river. Sampling was performed montly from May 2011 to April 2012 and replicated 3 times for each station. The NSFWQI, BMWP, ASPT and HBI indices were calculated based on the obtained data. The NSFWQI indicated that the water quality of Tajan River was in the “Poor” category. The BMWP index showed that the water quality was in the “Medium” category (for station 1, 2 and 3) and in the “Poor” category (for station 4). The water quality was placed in the “Suspected of pollution” and “Moderately polluted” categories by the ASPT index. HBI index pointed out that the water quality was in the “Relatively weak” and “Weak” categories. According to the results of this study, the water quality of Tajan River ranged from medium to very bad.