Jellyfish swarms forced a shutdown of France's largest nuclear facility at Gravelines, impacting 900-megawatt reactors but posing no safety risks to staff.

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.