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.

One of the largest French nuclear power plants was temporarily shut down after a swarm of jellyfish entered the water intake systems used to cool the coastal reactors, on Monday its operator said.

A massive jellyfish invasion clogged the cooling intake systems at France’s Gravelines Nuclear Power Station, forcing several reactors offline in a rare, non-nuclear shutdown.