Four reactors at France’s Gravelines nuclear power plant were shut down late Sunday due to a swarm of jellyfish in the cooling systems, operator EDF said on Monday, likely due to rising water temperatures because of global warming.

A swarm of jellyfish forced a nuclear power plant to shut down four reactors after the animals were found in the plant’s cooling systems. It was called a “massive and unpredictable presence of jellyfish,” The New York Times reported.

Four of the plant’s reactors shut down after swarms of jellyfish clogged its pumping stations. It isn’t the first time the creatures have thwarted nuclear plants.