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.

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 swarm of jellyfish caused the nuclear power plant to stop operating. According to foreign media such as the Daily Mail, the Gravlin nuclear power plant in northern France has been temporarily shut down due to the sudden appearance of a large swarm of jellyfish.