Introduction: There are natural and artificial radioactive nuclei in our environment, as well as in the structure of the living organism. Currently, industrial and municipal pollution has also an impact on increasing the level of radiation. The present study investigated the effect of inlet water from Arak Wastewater Treatment Plant on international Meighan Wetland and assessed the radiological indicators of sediments and water samples in this area. Material and Methods: In this study, the specific activity of radionuclides in water and sediment samples taken from the water entry areas of the international Meighan wetland was determined using a high purity germanium detector (Baltic Scientific Instrument LTD, 005- Latvia). Radiological indices for collected samples were calculated, and the topographical maps of radiation dose distribution were plotted using Surfer software (version 13). Results: Specific activities of 226Ra, 232Th, 40K, and 137Cs in sediment samples were in the range of 14.44-26.58, 22.78-34.56, 360.84-447.79, and 0.7-13.03Bq⁄kg, respectively. The average values of the external hazard index for sediment samples were calculated at 0.25. Conclusion: According to the obtained results, it can be concluded that pollution is more embedded in the Treatment Plant's basin, and a small amount goes to the wetlands. Radioactivity in the research area is normal, and topographic maps show that the distance from the entrance reduces the activity of radium and increases the activity of cesium. Assessment of hazard indicators showed that radiation levels in this area are not dangerous to human health.
