The global interest of the water bodies due to the water scarcity crisis encourages researchers to study the details water environment in different aspects. Consequently, this study objective to evaluate the water quality in the Euphrates River through adopted 11 physicochemical parameters measured at 16 locations during the 3 years (2009–2011) for both seasons (dry and wet). In this study, the water quality index model (WQIM) was calculated after modifying the weighted arithmetic method to define as MWQI. The chosen parameters were comprised of Cl, SO₄, HCO₃, NO₃, Na, K, Ca, Mg, TH, TDS, and EC. For the river section of locations (L.1–L.10), all readings of the selected parameters (expected HCO₃) were increased more and more. Then, all concentrations of parameters were recorded the high increasing after location (L.10) at locations (L.11–L.14). The concentrations situation of HCO₃ were verse vice at all locations. For the average values of 3 years (wet, dry, total), the MWQI of section length of the Euphrates River at locations (L.1–L.10) were classified as good water quality (class, C-II). The river section at locations (L.11–L.16, excepted L.13) was classified as poor water quality (class, C-III), while the location (L.13) was classified as very poor (class, C-IV). The interpolation prediction maps of the average readings (total, dry, and wet) of the Euphrates River were output in GIS using the interpolation model of IDWM.