The aim of this study is to investigate the distribution of pollution caused by natural and artificial radionuclides such as 226Ra, 232Th, 40K and 137Cs in the sediments and water of Miankaleh Lagoon in the north of Iran in the southeast of the Caspian Sea. The specific radionuclide activities of the water and sediment of Miankaleh Lagoon were measured using high purity germanium (HPGe) detector from Baltic Scientific Instruments (BSI) and maps of their distribution were obtained with GIS software version 10.3. The mean concentration of 226Ra, 232Th, and 40K was 16.06, 21.19 and 312.37 Bqkg− 1 and 1.13, 14.34 and 23.63 Bqkg− 1 for sediment and water samples, respectively. The mean concentration of 137Cs in sediment samples was 4.81 Bqkg− 1 . In the case of sediments, the highest concentration of 226Ra was observed in the southern part of the bay at the mouth of the Galougah River. The distribution map of 232Th showed a rapid deposition of this radionuclide at the mouth of the Gaz River. The highest concentration of 40K and 137Cs was observed in the area of the mouth of the Gaz River and the quiet part of the central region of the bay, respectively
