A nuclear power plant in France remains offline after an unusual incident in which a massive swarm of jellyfish clogged its cooling system.

According to French energy company EDF, the jellyfish overwhelmed pumps used to circulate water for cooling the reactors, forcing operators to shut down the facility as a safety precaution. The plant has been closed for more than a day while crews work to clear the blockage and assess any potential damage.

Such events, while rare, have occurred at coastal power plants around the world when large marine blooms disrupt intake systems. Experts say jellyfish swarms can be difficult to predict and are sometimes linked to changes in ocean temperatures and currents.

EDF has not provided a timeline for restarting the reactors, but stressed that there was no danger to the public or the environment.