Aygır Lake is located in the province of Bitlis, Adilcevaz, in the east of Turkey. It is located on the south side of Süphan Mountain and is a tectonically formed lake. Since the waters of Aygır Lake are fresh, it is an important water source in terms of meeting the water needs of the agricultural areas in the south. For this reason, it was tried to determine whether the water of the lake would pose a health risk in terms of radon if it was consumed as drinking water and used in agricultural activities and fish farming. In the study, radon (222Rn) concentrations, the annual effective dose rate (AED) and the amount of dose the stomach takes (SED) in the surface water samples taken from Aygır Lake were tried to be determined. For this purpose, water samples were taken from 13 different points in the lake. Saphymo Gmbh AlphaGUARD Professional radon monitor was used to measure the radon activities of the water samples. As a result of the measurements, it is seen that the radon concentrations vary between 0.15 ± 0.01 Bq L-1 and 0.71 ± 0.08 Bq L-1. In addition, in the study, AED values ranged from 0.38 ± 0.03 nSv y-1 to 1.81 ± 0.20 nSv y-1, while SED values ranged from 0.05 ± 0.00 nSv y-1 to 0.22 ± 0.02 nSv y-1. When the results obtained are compared with the average international values, it is noticed that the results are below these values.