Radioactivity measurements for water, sediment, microbial films and the bioaccumulation of radionuclides by extremophiles from hypersaline lakes and hot springs were carried out as scarcity studies in the Siwa Oasis, Egypt. Natural and man-made radionuclides were measured using high-resolution γ-spectrometry. Different radionuclides behaved differently in different environmental samples, while radionuclides were higher in microbial films compared to sediment, but all radionuclide levels except 226 Ra in water were generally low. Microbial films from hypersaline lakes had higher concentrations of 40 K, while microbial films from freshwater hot springs had the highest concentrations of 226 Ra, 232 Th and 137 Cs. The calculated radiological hazard index parameters of radium equivalent activity (Ra eq ), absorbed dose rate (D), annual effective dose (AED) and external hazard (H ex ) in the sediment were within acceptable limits, but were higher in the microbial film samples. Otherwise, the potential cancer risk of the three freshwater springs was 0.00244 ± 0.000293, 0.00135.6 ± 0.000172 and 0.00155.2 ± 0.000198. In addition, the bioaccumulation factor for microbial films indicated that they are good accumulators of radionuclides, especially for 226 Ra and 232 Th, which may contribute to their effectiveness in removing radionuclides from ecosystems.