Aims: The Meymeh River is fed by several tributaries, leading to a gradual decrease in its quality. Considering the construction of the Meymeh reservoir for agricultural use, it is necessary to monitor the spatial and temporal changes in water quality and to identify areas where river quality changes. Methods: Our method was based on the analysis of 420 samples over 12 months (2016–2017) in three seasons (low, moderate, and high flow periods) from 35 measuring stations using Spearman's correlation, multivariate statistical analysis, agglomerative hierarchical clustering, and GIS. Findings: The results showed that crossing the saline evaporite layers (especially the Gachsaran Formation) causes a gradual decrease in water quality from upstream to downstream. So, EC reaches from 400 to more than 3500 µm. cm-1 at the confluence of Varazan and Kharvazan tributaries. Besides, the sulfur spring with an average EC of 21590 µm. cm-1 increases EC 3.5 times. Siyoul tributary penetrates under the ground after passing through two saline zones and reappears at a distance of 150 to 200 m with an EC of 187800 µm. cm-1. It was also found that about 50% of the salinity of the Meymeh River is caused by the influence of the Ghadah Sulfur Spring and the Siyoul tributary. Conclusion: This study has highlighted some options for managing the level of salinity in the dam. In most cases, one option on its own may not have the desired effect, and a combination of techniques is likely to bring the best results.
