A female grey seal was rescued from Wylfa nuclear power station this week after getting trapped in one of the cooling chambers.
Staff at the Anglesey power station in Wales called the RSPCA to free the sea mammal.
The animal protection group said seals sometimes get sucked along by strong currents created by the power station and can slip through the bars at the end of the sea pipe.
The seal was returned to the sea further along the coast at Cemlyn Bay once it was given a “clean bill of health”.
RSPCA Inspector Mike Pugh said: “This kind of rescue happens from time to time and we’re grateful for the vigilance of power station staff.
“We’re really happy that this seal was unharmed by her adventure and we could return her safely to the sea”.
There were 124,000 grey seals in Great Britain in 2000 according to the Joint Nature Conservation Committee.
It’s not the first time an animal has thrown a spanner in the works at an energy plant. In October, jellyfish caused a Swedish nuclear plant to shut down after finding their way into the cooling water tank.