Water pollution is the most important reason to monitor and assess water quality. The chemical, physical, and biological quality of natural waters may be affected by anthropogenic activities such as industrial, urban, and agricultural activities. In the present study, the water quality of the Zarrineh River, one of the main rivers supplying water in the northwest of Iran, was investigated. A total of 21 sites were selected for surface water sampling during spring and winter (dry and wet) seasons. The concentrations of the metals aluminum, iron, barium, chromium, arsenic, copper, manganese, nickel, selenium, lead, and zinc were determined for source partition and heavy metal pollution index (HMPI) assessment during both the spring and winter seasons. Four important dominant factors in the principal component analysis depicted, in toto, 76.22 percent of the variance, with an initial eigenvalue greater than 1. The calculated HMPI for all the seasons and sampling stations was 66, fluctuating between 30 and 170 in single water sampling sites. The results showed that almost all locations fall into the high classes of the HMPI, but below the critical pollution index limit of 100. Apart from the gold mining establishments and industrial factories, the reasons for the increased concentrations of metals in the Zarrineh River may be attributed in particular to anthropogenic and mining activities.