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.

Electricite de France SA was forced to shut four atomic reactors after a swarm of jellyfish clogged up filter drums at its Gravelines power plant.

Operator EDF says the incident does not pose a threat to the safety of the plant, its workers or the environment.