In this study, 16 sediment samples were collected from Bree, Klein-Brak, Bakens and uMngeni rivers of South Africa and were prepared, analysed and evaluated for the activity concentration of 238U, 232Th and 40K concerning its radiogenic heat production using a high-purity germanium detector. The results show that 238U is the prevalent radionuclide in radiogenic heat production, with 232Th and 40K emerging as trace elements. The mean activity concentrations are 28.97%, 63.69% and 7.34% for uranium, thorium and potassium, respectively, from all sampling locations. This shows that a high radioactive concentration of a specific radionuclide does not necessarily imply its increased contribution to radiogenic heat production. The radionuclide contributions to radiogenic heat production at all sampled locations are 59.39%, 35.11% and 5.50% for uranium, thorium and potassium, respectively. The mean radiogenic heat production rate in the study area ranged from 0.0180 μW m − 3 in sediment samples from the Bree River in Western Cape to 0.0072 μW m − 3 in sediment samples of uMgeni River in KwaZulu-Natal. All values obtained for this study are five times lower than the average continental radiogenic heat production of 1 μW m − 3 . This study provides insight into the radiogenic heat production rate due to the presence of radionuclides in all river samples.