Two men found what was thought to be a World War One grenade while they were magnet fishing in a canal.
Rob Trowler and Gaz Thomas hauled the rusted device from the water near Tarleton, Lancashire.
People were diverted away from the area before the grenade was moved to a nearby field where a controlled explosion was carried out by army bomb disposal officers.
The Canals and Rivers Trust said magnet fishing was dangerous.
Attended an incident earlier in Tarleton. Only a few minutes from the station on foot. 2 magnet fisherman had found a WW1 grenade. Cordon in place and EOD notified. Here's the video of EOD disposing of the device in a nearby field.— LancsSpecials (@LancsSpecials) July 4, 2019
T/S/INSP Stephen pic.twitter.com/eiLbqxv9N8
The pair alerted police after making the discovery in the Rufford Branch of the Leeds and Liverpool Canal at 15:15 BST on Thursday while trawling for scrap metal.
Mr Trowler, 30, said he believed it was a grenade manufactured by Mills Munitions.
"I couldn't believe it," he said
"I thought it was a grenade straight away and showed it to my friend who agreed we'd need to ring the police."
Mr Trowler said he went magnet fishing with Mr Thomas, 29, "a couple of times a week" and the pair had found items including "a sword, cannonballs, motorbikes and bags of coins".
He said the hobby was not dangerous "if you use common sense".
The Canals and Rivers Trust said it had seen a spike in reports of magnet fishing, but warned it was dangerous to pull objects out of the water.
In June 2018, a man and his son died in Huddersfield while magnet fishing.
The Ministry of Defence told the BBC it dealt with devices found by magnet fishermen on a regular basis.