Jellyfish may be spineless, but they showed the backbone of a dedicated environmentalist over the weekend. A swarm of the gelatinous sea dwellers overwhelmed a nuclear power plant in northern France, forcing its shutdown on Sunday.

Four of the plant’s reactors shut down after swarms of jellyfish clogged its pumping stations. It isn’t the first time the creatures have thwarted nuclear plants.

Four reactors at France’s Gravelines nuclear power plant were shut down late Sunday due to a swarm of jellyfish in the cooling systems, operator EDF said on Monday, likely due to rising water temperatures because of global warming.