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.

A French nuclear plant temporarily shut down on Monday due to a "massive and unpredictable presence of jellyfish" in its filters, its operator said. The swarm clogged up the cooling system and caused four units at the Gravelines nuclear power plant to automatically switch off, energy group EDF said.