Since its inception, nuclear energy has faced a host of opposition, from oil conglomerates to well-intentioned anti-nuclear-weapons activists to environmental groups. As it turns out, even ocean critters are getting in on the movement.

Four reactors at France's Gravelines nuclear plant will return to operation throughout the week, slightly later than initially planned, EDF data showed on Tuesday, after they were forced offline by a swarm of jellyfish in the cooling systems.

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.