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The study is based on data covering the water, sediments, plants and fish sampled over a 20-year period at 15 stations along French rivers. Three geographic zones were investigated: one containing a uranium mining complex (Zone 1), another including five major rivers along which nuclear power plants are sited (Zone II) and a third unaffected by nuclear activities (Zone III). Natural radioactivity basically involves 238U, 226Ra and 210Pb in the uranium series, 232Th from the thorium series, 40K and 7Be. The natural radioactivity in Zone II is not different from Zone III, and is thus unaffected by waste discharges from nuclear power plants. The most abundant radionuclide is 40K, while the other nuclides are often found in trace amounts near the detection threshold of the analysis method used (Ge gamma spectrometry with a 15-hour counting period). The 226Ra and 238U concentrations observed in Zone I are at least an order of magnitude higher than in the other two zones due to authorised waste discharges from the Lodève mining complex, but only a small stream is affected. The measured 226Ra concentrations would result in an annual whole body committed dose equivalent attributable to a 200 g weekly fish consumption from this stream of 4.4 x 10-5 Sv.y-1, or 0.86% of the maximum permissible dose (5 mSv).