Four units at the Gravelines nuclear power plant in northern France shut down today due to the “massive and unforeseen presence of jellyfish” at water pumping stations used to cool the reactors, the electricity company EDF announced.

These automatic shutdowns of units 2, 3, 4, and 5 “had no impact on the safety of the facilities, the safety of staff, or the environment,” EDF assured in a statement on its website.

As a result, the plant has temporarily closed entirely, since its other two production units, 1 and 6, are currently under maintenance.