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.

A nuclear plant in northern France was temporarily shut down on Monday after a swarm of jellyfish clogged pumps used to cool the reactors, energy group EDF said.

Located on the Channel coast near Dunkirk, Gravelines is the largest nuclear power plant in western Europe, with six 900 megawatt reactors.