A “massive and unpredictable” swarm of jellyfish has caused one of the largest nuclear power plants in France to completely shut down.

According to the Guardian, the jellyfish swam into water intake systems at the Gravelines facility in Northern France. The resulting clog in the filters caused four of the plant's six pumping stations to cease operation. The other two were already shut down for maintenance, leaving the systems needed to cool the reactors completely offline.