The current situation of freshwater pollution is worrying, Due to the limited fresh water resources and the increase in population and the expansion of cities and the development of industry and agriculture around the rivers, it is necessary to use the available resources correctly. Heavy metals are one of the non-degradable and important pollutants that exist in water, sediments and living organisms. These elements are present both in natural sources, weathering of mineral rocks and seepage from the soil, and anthropogenic sources stemming from human activities. In this study, 45 water samples of the Karun River from 5 different stations were analyzed by an Atomic Absorption Spectrometer device (AAS) for lead, mercury and cadmium content. The results show that the highest amount of pollution is related to station number 1 and the lowest amount of heavy metal pollution is related to station number 5. Pollution decreases from station number 5 to station 5. According to the results of the indices: metal index (MI), heavy metal pollution index (HPI) and degree of pollution (Cdeg), the water of the Karun river in the study area is polluted with heavy metals, some samples have moderate pollution and some They have a high degree of pollution and are undrinkable. Statistical analysis also shows that the pollution of the Karun River is not from a single source and it is possible to look for the lithology of the area (natural factor) which should be traced to the formations upstream of the dam, as well as human activities in the area (human activities). Named as the main factors of pollution.