The paper presents the activity concentrations of 232Th, 226Ra and 40K in the sediments and river bank soil samples collected from the Kallada river environs of coastal Kerala. The radiological risks associated with these radionuclides were calculated. The samples were processed following standard procedure, and activity was counted using a high-efficiency 5″ × 5″ NaI (Tl) detector coupled to GSPEC gamma spectroscopy system. The mean values of measured activities of 232Th, 226Ra and 40K in soil samples were found to be 98.1 ± 0.4, 60.3 ± 1.1 and 343.4 ± 1.8 Bq kg−1, respectively, which results in an average absorbed dose rate of 103 nGy h−1. The corresponding values for sediment samples were found to be 88.0 ± 0.4, 48.6 ± 0.9 and 423.2 ± 2.0 Bq kg−1, respectively, with a resulting absorbed dose rate of 95 nGy h−1. Radium equivalent activity, annual effective dose equivalent, the external and internal hazard indices were determined and compared with recommended limits. The results of the work provide background data on natural radioactive isotopes, which are useful in the assessment of human radiation exposure from natural environment. The accumulation of information on natural radiation is of great value for radiation protection.