Getty ImagesA 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.
The site in northern France was shut after the incident, with its remaining two units already down for maintenance.
EDF said there had been "no impact on the safety of the facilities, the safety of personnel, or the environment".
It added that the fish were found "in the non-nuclear part of the facilities".
"The plant teams are mobilised and are currently carrying out the necessary diagnostics and interventions to be able to restart the production units safely," EDF said in a statement.
Situated between Dunkirk and Calais, Gravelines is one of France's largest power plants, with six units which each produce 900 megawatts of power.
It is cooled from a canal connected to the North Sea, where several species of jellyfish are native and can be seen around the coast when the waters are warm.
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