Army bomb experts have carried out a controlled explosion on a World War Two mortar shell at Murlough beach, County Down.
In a tweet, the South Down Coastguard said the mortar "was high explosive and was fused".
It was discovered by two dog walkers on Sunday who sent a photograph to the coastguard.
The couple stayed close to the site to pinpoint the location to the coastguard.
Police arrived shortly afterwards and sealed off a section of the beach between Murlough and Newcastle.
Dawn Mitchell, an artist from Hillsborough, County Down, was on the beach with her husband and dogs, taking photographs of the Mourne Mountains from Murlough beach, when they spotted the rusted object.
She said her dogs were playing in the sea when one of the animals jumped out of the water suddenly.
Mrs Mitchell looked down into the water to find out what had frightened her dog and saw what she thought was a "big fish".
She said her husband "poked at it with a stick" but then stepped back and shouted: "It's got fins - it's a mortar".
The couple phoned the coastguard to report their discovery as there were other members of the public on the beach.
Mrs Mitchell said the coastguard asked her to take a photograph of the object to ensure they were not about to spark a false alarm, unintentionally.