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.

A French nuclear plant temporarily shut down on Monday due to a "massive and unpredictable presence of jellyfish" in its filters, its operator said. The swarm clogged up the cooling system and caused four units at the Gravelines nuclear power plant to automatically switch off, energy group EDF said.