Both reactors at a nuclear power station have been shut down after "high volumes" of jellyfish were found on seawater filter screens.
The units at Torness power station, on the coast near Dunbar in East Lothian, were closed down manually on Tuesday.
EDF Energy, which operates the plant, said the reactors were shut down as a precautionary measure and there was no danger to the public at any time.
The screens filter out debris in cooling water which enters the plant.
An operation is under way to clear the jellyfish from the waters near the power station and the reactors will be restarted once their numbers have gone down.
An EDF spokesman said: "Reduced cooling water flows due to ingress from jellyfish, seaweed and other marine debris are considered as part of the station's safety case and are not an unknown phenomenon.
"This was a precautionary action and the shutdown cooling systems performed in a satisfactory manner and both reactors were safely shut down. At no time was there any danger to the public. There are no radiological aspects associated with this event and there has been no impact to the environment."
EDF Energy could not comment on when the reactors are likely to be started up again. The Office of Nuclear Regulation (ONR) has been fully briefed about the incident.
Earlier this month an Atlantic grey seal was rescued after it became trapped in a nuclear power station's water intake chamber. Workers at EDF Energy's Hinkley Point B site in Somerset spotted the seal swimming around in the pool of water.
Although the mammal, named Celia by staff, was unharmed, she was unable to swim out by herself. After being rescued and checked by a vet she was released from a beach a few miles west of the power station.