Four of the six nuclear reactors at France's Gravelines nuclear power plant were shut down after an intake pipe used to draw water for cooling from a canal became clogged with jellyfish, Reuters reported.

During a jellyfish bloom, there is too much biomass at once. The screens clog, water flow drops, and pumps start to strain. Under pressure, jellyfish can also break into a thick gel that slips through meshes and fouls equipment downstream.

A nuclear power plant in northern France hit by a jellyfish invasion was getting back online on Wednesday, operator EDF said, with service restored at the first of four closed reactors.