A massive jellyfish swarm clogged the cooling water intake at France’s Gravelines nuclear power plant, forcing all four reactors offline late Sunday.

Three reactors shut down automatically, while a fourth was already offline for maintenance.

EDF said there was no safety risk or impact on power exports.

The North Sea–fed plant, which can power 5 million homes, joins a long list of coastal facilities worldwide — from Scotland to China — disrupted by sudden jellyfish blooms, The Guardian has reported.

Scientists have been developing early-warning tools to predict such swarms.

Written by B.C. Begley