The statistics of 4 quantitative and qualitative sampling stations of the region were used to investigate the water quality status of the Gamasiyab River in the Nahavand subbasin in the west of Iran. The statistical period used in this study is 54 years (from the water year 1969-70 to the water year 2022-23). In this study, the chemical quality of surface water sources in the Nahavand subbasin in the Karkheh basin has been investigated and analyzed using the results of qualitative analysis of water samples at water measuring stations. To be able to have a more detailed analysis of the quality of surface water in this subbasin, the water quality was examined in different time scales including ten-year, seasonal, annual, and the entire statistical period. Also, to check the quality situation in terms of drinking, agriculture, and industry, and check for corrosiveness used the Wilcox diagram, Schuler diagram, indexes of electrical conductivity (Ec), sodium percentage (SP(Na%)), sodium absorption ratio (SAR), magnesium hazard (MH), permeability index (PI), kelly index (KI), Residual Sodium Carbonate (RSC), Langelier Index (LI), Reisner Index (RI), Aggressive Index (AI) and Pocorios Index (PI). The results showed that the qualitative status of all stations in all time scales is good qualitative status in terms of indexes of MH, KI, and RSC. Examining the results showed that, in general, the water quality status of the studied stations is suitable in terms of various indicators for drinking, agriculture, and industry