The Gorgan Rod River, located in northern Iran in Golestan Province, is the largest watershed in the province, which its water quality is affected by natural and anthropogenic changes. Water samples were taken between 1984 and 2008 from 18 sampling stations, along the Gorgan Rod River. Determination of non-principal and principal monitoring stations was carried out for the Gorgan Rod watershed, south-east of the Caspian Sea. Water quality parameters including EC, TDS, bicarbonate, carbonate, chloride, total hardness, calcium, potassium, sodium, sodium adsorption ratio, sulfate, pH, and magnesium were measured. The graphic representations obtained underline that (i) PCA (principal component analysis) is associated with the natural and anthropogenic changes in the different stations; and (ii) the locations of the different stations studied are consistent with their apparent features. The results indicated that water quality in Basir Abad, Agh Ghala, Haji Ghochan, and Bagh Salian stations was of the poorest among other stations because of anthropogenic effects. The best water quality was observed in Ramian, Araz Kose, Nawda, Pas Poshtah, Lezore, Glikesh, and Tangrah stations because there were no changes in land uses.