Electricite de France SA said it shut four of the six reactors at its Gravelines nuclear station in northern France after a sudden bloom of jellyfish clogged filter drums that draw seawater used to cool the reactors. The automatic shutdowns late 10 Aug and early 11 Aug triggered standard safety protocols and, according to the utility, posed no risk to staff, the public or the environment. The stoppage removed about 3.6 gigawatts of generating capacity—roughly two-thirds of Western Europe’s largest atomic plant—at a time when a heatwave is already straining cooling systems across the French nuclear fleet. EDF initially planned to have all four units back online on 12 Aug but revised the timetable: Unit 6 is now due to restart on Tuesday, with the remaining reactors scheduled to follow one per day through Friday. Marine biologists said the swarm consisted of native English Barrel jellyfish, whose numbers can spike when sea temperatures rise. Gravelines experienced a similar shutdown in 1993, and plants in Scotland, Sweden and Japan have faced comparable events. Scientists warn that warmer waters, overfishing and invasive species could make jellyfish-related disruptions more frequent.