Bomb disposal experts carried out a controlled explosion of a piece of Second World War ammunition after a father and son found it while magnet fishing.
Neil Grout, a 41-year old bricklayer, and his 10-year-old son Harry dredged up the mortar bomb while using a powerful magnet to search for items in the River Wensum at Attlebridge, near Norwich.
They initially thought it was an old aerosol can, but became suspicious that it might be something more dangerous so called the police.
They were told to immediately move away from the item and officers were sent to the scene.
They cordoned off the area before members of the army's Explosive Ordnance Disposal unit carried out the controlled explosion.
Mr Grout said they had only decided to go magnet fishing at the last moment, on bank holiday Monday.
"We haven't been for ages because it's quite grubby and you have to take everything home with you," he said.
"But that morning my son was really keen to go and he found the place we went on Google.
"I didn't get anything good but then he had a go and got something.
"We thought it might be an aerosol can at first but it was so heavy."
The item the pair, from Hevingham, found is believed to be a Second World War, British-made 2-inch mortar bomb.
Mr Grout said: "We wondered if it could be something like that so we called the police who told us to stay away from it.
"My son thinks it's all so exciting.
"It's definitely the best thing we've ever found."
It is not known how the item got into the Wensum.
During the Second World War, the area was a hive of military activity after the air force opened an airbase, RAF Attlebridge, nearby.
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