Two litter-pickers unwittingly drove half a mile (0.8km) home with a live World War One bomb on the car seat.
Rachel Wills and Simon Briscombe found the device during a clean-up at the River Nidd in Knaresborough on Monday.
When they "scraped the gunk" off what they had thought was a gas cannister, they realised it was an explosive and called the bomb squad.
Speaking after the Army had safely detonated the device, Ms Wills said it was "so lucky children didn't find it".
Ms Wills said she and her partner picked up litter along a stretch of river from the Watermill Cafe, which she owns, to Grimbald Bridge, every Monday.
She said: "We've found some really strange things, including a sewing machine from 1898, trolleys, money, shoes, all sorts.
"But I can't believe we found what we found and it was live," she said.
"We had it in our car, a live bomb, and we were driving over speed bumps too."
Ms Wills said she thought the recent floods had disturbed the bomb and brought it to the surface.
The cafe owner said as soon as the mud was removed she and Mr Briscombe saw what it was and called the emergency services.
'Frothing and bubbling'
The couple then photographed the bomb, wrapped it inside sandbags and waited while the bomb squad, police and firefighters, arrived at the scene.
Ms Wills said the wait was an anxious one: "It was frothing, the shell was bubbling. It was strange and frightening."
When emergency crews arrived, the couple's house on The Chase in Knaresborough and about 30 others on the estate, were immediately evacuated, Ms Wills said.
A 328ft (100m) cordon was put in place while an Explosive Ordnance Disposal (EOD) team attended to remove the object and safely dealt with it, police said.
"Thankfully, the EOD were able to dispose of the object and the incident was brought to a safe conclusion," the North Yorkshire force added.
The nearby A59 was also closed for about two hours.
Officers have since thanked members of the public for remaining calm and for being patient while the device was dealt with.
Ms Wills said she had been "tired, shocked and teary" since seeing the bomb explode, adding: "We had a narrow escape."
She said: "Imagine if children had found it, picked it up and thrown it about. It's unthinkable."
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