Rivers, as vital arteries of surface water, play an important role in providing various water consumption needs. Population growth and vast urbanization carry out a significant increase in the production of sewage and urban effluents, thus resulting in a decreasing river water quality rate. In this study, the impact of the agriculture wastewater sector (gardens), villages, restaurants, and tourist sites of the study area on the Abbas-Abad River water quality was investigated using the QUAL2Kw model. The modeling result of the period 2021-2022 showed any increase in pollutant flow realized by the agriculture sector and restaurant wastewaters increased the biochemical oxygen demand value of the river, especially in spring and summer. As a result, the amount of dissolved oxygen along the river, especially in the downstream sections (the end of considered river reach), decreased. Additionally, the river water illustrated an alkaline condition (high pH rate), and increased electrical conductivity (because of lack of sedimentation of dissolved and suspended solids) along the river. Although the nitrate rate was increased along the river during spring and summer, it did not also exceed the standard level for surface waters. The results of this research indicate a need to establish quality management of the river to have a safe environmental balance development that prevents the pollutant rate of the river, ensuring a sustainable trend in its self-purification value.