In this study, the specifc activity of radionuclides was measured using a high purity germanium detector (HPGe) and the distribution pattern of radiological parameters and hazard indicators was plotted using Surfer and GIS software. Sediment samples were collected from the Gaz River in the mountains of Golestan province, and the central and southern part of Gorgan Bay. In the samples, the average values of specifc activity of 226Ra, 232Th, 40K and 137Cs are 17.61, 35.91, 398.65 and 4.01 Bqkg−1 , respectively. The highest concentration of 40K is in the sediments of the outlet of the Gaz River, which may be due to the use of potassium fertilizers for agricultural activities in this area. The concentration of 137Cs activity in the Bay sediment is higher than other sediments, also due to the high mobility and lightness of 137Cs, higher concentration of this radionuclide is in the quiet parts in the middle of the bay. In Gorgan Bay, the maximum of radiological parameters is in the estuary of Gaz River and in line with the water fow, the maximum level of these parameters tends to northwest. Mean radiological indices such as Raeq, Dose, AEDout, ELCRout and AGDE estimated as 99.67 Bqkg−1 , 45.82 nGy/h, 0.056 mSvy−1 , 0.197×10−3 and 329.72 µSvy−1 , respectively which they were all within the allowable range and not threaten the health of residents.
