Narrow boat owner Reuben Chesters was moored a few feet away from the boys who were fishing under the Viewforth Bridge when they made the discovery. Uniformed police officers attended a short time later to interview them.
Mr Chesters, 34, said: “I could see they had pulled something out of the water of interest and could see the shape was a gun. Police took it into a poly (polythene) bag.
“I shouted over after the police went away and they said they found a shotgun and had pulled out some bullets.
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“It was a small shotgun. It looked about a foot long with a small bend at one end and was quite dark. I was about 15 metres away but moored on the other side from where they were fishing. They were under the bridge.
“I had noticed the boys were magnet fishing before the police turned up, as I have got a magnet in case I drop something in the canal.
“It was a bit of a surprise to see it (the gun) but not a surprise, too, as you imagine that is where someone would chuck a weapon. It could have been chucked in there any time in the last 100 years. The police did not come back so I doubt it’s part of any active investigation.”
Mr Chesters, who runs a social enterprise called Locavore which focuses on food sustainability, said the teenagers returned with more friends or family on Saturday to try and find more objects in the water.
He said he is living on his narrow boat at the moment but spends time both in Edinburgh and Glasgow, where his Locavore shops are based.
A Police Scotland spokesperson said: “Officers were called around 6.10pm on Thursday, 8 July, 2021, to a report of a suspected firearm being pulled out of the Union Canal near Viewforth, Edinburgh.
"It was removed to a safe place and enquiries into its origins are ongoing.”
It is not the first time that magnet fishers have found weapons in canals.
In August last year, Andrew Whiteman described his shock after finding a revolver, machete and two submachine guns wrapped in plastic bags from a stretch of the Leeds and Liverpool Canal in Burnley. He also found two other guns near the same spot.
Around the same time last year, a group of magnet fishers pulled out a cache of weapons - including machetes and a gun - from the Forth and Clyde Canal in Glasgow.
Magnet fishing is similar to metal detecting and involves using magnets attached to the ends of ropes to recover metal objects dumped in canals and rivers.
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