Water quality assessment is one of the most important research and implementation issues in the world. Load continuity curve is a method that can achieve favorable results with less data in the field of determining the quality conditions of the river and its influencing factors. In this research, LDC curves were used to determine the pollutant sources affecting the Tajen River. First, with the help of probability distribution functions and stream discharge information (18 years), the best curves of flow continuity in two hydrometric stations including Rig Cheshme and Kordkhil were drawn, and then the curves of the maximum allowable load of nitrate pollutant for two agricultural uses and water ecosystem in the cultivation and non-cultivation seasons were created. Then the LDC curves were drawn for the 8-year period from 1390-91 to 1397-98.The results showed that in the area of Rig Cheshme station, most of the non-point sources affect the nitrate pollution of the river, however in Kordkhel station, due to the occasional increase in the amount of nitrate pollution for minimum discharges in the cultivation seasons, it was determined that non-point sources are the cause of this increase. The results of this study showed the favorable ability of load continuity curves in determining the origin of pollutant load. On the other hand, with the investigations done and according to the quality conditions of the river from Kordakhil station to the mouth of the Tajen river, it was found that the river is more polluted than the permissible limit near the mouth during the cultivation seasons. Therefore, the revision of the calculations of releasing the flow from the Shahid Rajaei dam, the optimal water consumption in the river, and the management of the application of nitrogen fertilizers in the lands of the region should be considered.Water quality assessment is one of the most important research and implementation issues in the world. Load continuity curve is a method that can achieve favorable results with less data in the field of determining the quality conditions of the river and its influencing factors. In this research, LDC curves were used to determine the pollutant sources affecting the Tajen River. First, with the help of probability distribution functions and stream discharge information (18 years), the best curves of flow continuity in two hydrometric stations including Rig Cheshme and Kordkhil were drawn, and then the curves of the maximum allowable load of nitrate pollutant for two agricultural uses and water ecosystem in the cultivation and non-cultivation seasons were created. Then the LDC curves were drawn for the 8-year period from 1390-91 to 1397-98.The results showed that in the area of Rig Cheshme station, most of the non-point sources affect the nitrate pollution of the river, however in Kordkhel station, due to the occasional increase in the amount of nitrate pollution for minimum discharges in the cultivation seasons, it was determined that non-point sources are the cause of this increase. The results of this study showed the favorable ability of load continuity curves in determining the origin of pollutant load. On the other hand, with the investigations done and according to the quality conditions of the river from Kordakhil station to the mouth of the Tajen river, it was found that the river is more polluted than the permissible limit near the mouth during the cultivation seasons. Therefore, the revision of the calculations of releasing the flow from the Shahid Rajaei dam, the optimal water consumption in the river, and the management of the application of nitrogen fertilizers in the lands of the region should be considered.Water quality assessment is one of the most important research and implementation issues in the world. Load continuity curve is a method that can achieve favorable results with less data in the field of determining the quality conditions of the river and its influencing factors. In this research, LDC curves were used to determine the pollutant sources affecting the Tajen River. First, with the help of probability distribution functions and stream discharge information (18 years), the best curves of flow continuity in two hydrometric stations including Rig Cheshme and Kordkhil were drawn, and then the curves of the maximum allowable load of nitrate pollutant for two agricultural uses and water ecosystem in the cultivation and non-cultivation seasons were created. Then the LDC curves were drawn for the 8-year period from 1390-91 to 1397-98.The results showed that in the area of Rig Cheshme station, most of the non-point sources affect the nitrate pollution of the river, however in Kordkhel station, due to the occasional increase in the amount of nitrate pollution for minimum discharges in the cultivation seasons, it was determined that non-point sources are the cause of this increase. The results of this study showed the favorable ability of load continuity curves in determining the origin of pollutant load. On the other hand, with the investigations done and according to the quality conditions of the river from Kordakhil station to the mouth of the Tajen river, it was found that the river is more polluted than the permissible limit near the mouth during the cultivation seasons. Therefore, the revision of the calculations of releasing the flow from the Shahid Rajaei dam, the optimal water consumption in the river, and the management of the application of nitrogen fertilizers in the lands of the region should be considered.