The super(226)Ra and super(228)Ra activities of Qinghai Lake surface water, groundwater, river water, suspended particles, and bottom sediments were measured in a gamma-ray spectrometer. The sources of super(226)Ra and super(228)Ra were discussed according to their distribution characteristics. super(226)Ra and super(228)Ra activities (dpm/(100 L)) ranged from 14.13 plus or minus 0.22 to 19.22 plus or minus 0.42 and 17.72 plus or minus 0.66 to 30.96 plus or minus 1.47 in the surface water of the North Bay, respectively, and from 7.88 plus or minus 0.24 to 33.80 plus or minus 0.47 and 15.73 plus or minus 0.74 to 57.31 plus or minus 1.44, respectively, in the South Bay. The surface water near the estuary had a lower salinity and had a higher concentration of radium isotopes than the samples collected further away. The farther offshore the sample, the higher the salinity was, and the lower the radium isotope activity. The distribution of radium activities in the western part of Qinghai Lake is controlled by several factors, including Buha River runoff, desorption from suspended particles derived from the river, groundwater discharge, and a small amount of diffusion from the sediment.