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.

Four of the six nuclear reactors at France's Gravelines nuclear power plant were shut down after an intake pipe used to draw water for cooling from a canal became clogged with jellyfish, Reuters reported.

Last weekend, a surprising and uncommon issue arose at one of the biggest nuclear power facilities in Europe. It was not a storm, a technical breakdown, or a security threat. Instead, it was an invasion of jellyfish that forced part of the facility to stop operations.