William Hartley got a magnet fisher for Christmas, and was testing it out with his grandad Nick on the canal near his Hest Bank home when he made the shocking find.
The magnet hangs from a length of rope around 20m long, and after a few days fishing and catching old anchors and hammer heads, it was a bit of a surprise for William to pull out a World War One bomb shell.
Dad Andrew said: "The magnet fisher was the first thing he wanted for Christmas, and he was desperate to go out to use it.
"He loves being outdoors and going off on adventures with his grandad in the woods.
"They had gone to the canal, and he was sending me back pictures of some of the things he had caught.
"Then he suddenly rang me and said he was bringing something home but couldn't bring it in the house.
"We waited outside and could see him with this bomb and I just wondered if he should be bringing it home! It was a real shock."
Andrew put the bomb in the garage but later decided to contact the police.
"I was thinking there was something not quite right so I asked a neighbour who said I should call the police," he said.
"They came and had a look at it and said that the top part was still intact and hadn't gone off. They asked us to clear away from the area, and then another police car turned up and they took photos to email off to be checked.
"It came back that they were 20 per cent unsure so they would have to get the bomb disposal unit out.
"I was wondering if this was real!"
Fortunately the area didn't have to be evacuated, although the family had to be prepared for any eventuality.
The bomb squad was called in from Chester, arriving just before midnight - and found William waiting to see them.
"They said the top part was a timer that hadn't gone off and they had to take it away to destroy it themselves, because it hadn't properly detonated," Andrew said.
"They were really helpful and told William all about it and that they thought it was from World War One.
"It had to be locked up in the van, and they showed William inside the van and what they were doing.
"They were all so nice to William and explained it all, and they were impressed with his magnet. He found it all fascinating.
"All the neighbours were looking out of their windows at what was happening, it was crazy."
Andrew said William couldn't wait to return to Slyne-with-Hest Primary School this week to tell everyone about his discovery.
"This was a Christmas he will never forget," he said.