A nuclear power plant in northern France hit by a jellyfish invasion was getting back online on Wednesday, operator EDF said, with service restored at the first of four closed reactors.

Located on the Channel coast near Dunkirk, Gravelines is the largest nuclear power plant in western Europe, with six 900 megawatt reactors.

Four reactors at France’s Gravelines nuclear power plant, located along the English Channel, were temporarily shut down over the weekend after a swarm of jellyfish threatened to clog critical water intake systems.