en Environmental Health, Sciences, and Engineering Environmental Health, Sciences, and Engineering پژوهشي Original Article <div style="text-align: justify;"><span style="line-height:1;"><span style="font-size:14px;"><span style="font-family:Times New Roman;"><b><span style="color:black">Background:</span></b><span style="color:black"> Water quality is increasingly threatened by human activities and the impact of climate change. In this study, the water quality of the Haraz, Tajan, and Cheshmeh Kileh Rivers in Mazandaran Province was evaluated using three widely recognized and reliable water quality indices.</span><br> <b><span style="color:black">Methods:</span></b><span style="color:black"> Physicochemical data obtained from samples collected at specified stations during 2021 and 2023 were analyzed. The evaluated parameters included dissolved oxygen, biochemical oxygen demand, pH, turbidity, nitrate, phosphate, temperature, total coliforms, and total dissolved solids.</span><br> <b><span style="color:black">Results:</span></b><span style="color:black"> The results demonstrated that the National Sanitation Foundation Water Quality Index (NSFWQI) and Iranian Water Quality Index (IRWQI) generally classified the water quality of the Haraz, Tajan, and Cheshmeh Kileh Rivers as Moderate to Good, whereas the British Columbia Water Quality Index (BCWQI) categorized several stations as falling within the Poor category. This outcome is consistent with findings from national and international studies, which indicate that the BCWQI tends to be more stringent and sensitive to deviations from established water quality standards.</span><span style="color:black"></span><br> <b><span style="color:black">Conclusion:</span></b><span style="color:black"> A comparison of the present study with domestic and international research validates the reliability of the results and confirms that the observed differences among the indices (especially the greater sensitivity of BCWQI) are fully consistent with global observations. These similarities indicate that the use of the Water Quality Index (WQI) in surface water studies can well reflect spatial and temporal changes in river water quality in humid regions with a temperate climate, such as Mazandaran Province.</span></span></span></span></div> Physicochemical water quality parameters, Environmental monitoring of rivers, Northern Iran water quality monitoring, WQI, 0 0 http://jhehp.zums.ac.ir/browse.php?a_code=A-10-122-11&slc_lang=en&sid=1 Mehrtaash Gholinezhad mehrtaash@gmail.com 100319475328460016387 0009000818287990 No Department of Watershed Engineering, Faculty of Natural Resources, Sari Agricultural Sciences and Natural Resources University, Sari, Iran. Kaka Shahedi k.shahedi@sanru.ac.ir 100319475328460016388 0000000337939954 No Department of Watershed Engineering, Faculty of Natural Resources, Sari Agricultural Sciences and Natural Resources University, Sari, Iran. Abbasali Zamani Zamani@znu.ac.ir 100319475328460016389 0000000182831235 Yes Department of Environmental Sciences, Faculty of Sciences, University of Zanjan, Iran. Ghorban Vahabzade kabria gh.Vahabzade@sanru.ac.ir 100319475328460016390 0000000182014681 No Department of Watershed Engineering, Faculty of Natural Resources, Sari Agricultural Sciences and Natural Resources University, Sari, Iran. Seyed Ramazan Mousavi srmmousavi@gmail.com 100319475328460016391 0000000221575458 No Department of Watershed Engineering, Faculty of Natural Resources, Sari Agricultural Sciences and Natural Resources University, Sari, Iran.