[en] Since the end of the 1970s a global method has been developed and improved to characterise the radioecological impact of French nuclear power plants (PWRs) on the marine ecosystems. The environment of every nuclear plant is examined yearly, in addition to special studies carried out before plant operations begin and after each period of ten years. Three nuclear power plants are situated on the Channel coast (Flamanville, Paluel, Penly) and one on the North Sea coast (Gravelines). Near the power plants local radioecological impact is measurable and is essentially due to ⁵⁸Co, ⁶⁰Co and ¹¹⁰Agm. The monitoring of artificial gamma-emitter radioactivity in bioindicators (Fucus sp.) reveals the overall decline in releases from the four power stations in question (⁵⁸Co, ⁶⁰Co and ¹¹⁰Agm) as well as the more marked decrease in relation to the reprocessing plant at La Hague (¹⁰⁶Ru, ⁶⁰Co, ¹²⁵Sb, ²⁴¹Am). (author)