They came across a grey metal object sticking out of the stretch of river between the Waterfield Leisure Centre and the Lady Wilton Bridge.
Chairman of the society Mick Clowes said: “We were flabbergasted. We thought it was a fridge freezer or a filing cabinet. Closer examination revealed it was a stolen safe.
“We could see from the tracks in the park and the big indent in the bank that someone had tipped the safe off the back of a van or lorry and it bounced its way down into the river.
“The attempts at opening it had seemingly been unsuccessful. The back of the cabinet was partially off but they hadn’t got into the inner sanctum.
“I’m sure I was told that the police officer who came thought the safe had been stolen from a card shop in town.”
The back of the cabinet was open enough for the society’s ‘Mole’ river clearance boat to get a hold of the safe with its bucket and recover it to the bank side before the police were called and the safe was removed.
The safe was recovered during the society’s work party around the ‘Melton ring’ on Sunday, January 24.
A Leicestershire Police spokeswoman said: “We had received a report of a burglary at a store in Cheapside overnight on December 17. A safe had been stolen from the premises.
“We later received information about the safe being recovered from the river. Forensics were looked into but no arrests have been made and there was nothing inside the safe.”
The Melton and Oakham Waterways Society currently have three river clearance boats - Mole, Badger and their latest addition ‘Toad’ - a steel craft, about 12-feet long, which was donated by workshop staff of Pillings Lock Marina in Quorn.
Mole was again called into action recently after the Melton Mowbray Town Estate asked for the society’s help in removing an old broken concrete, stone and brick step from the river.
Mr Clowes said: “Little did we know how big this lump would be!
“We estimated the weight to be about one-and-a-half tonnes which is around the maximum weight capacity of the Mole lifting gear.
“But she did us proud and we all breathed sigh of relief when the leviathan was safely on the bank.”
l For more information about the society and the projects they’re involved in visit www.meltonwaterways.co.uk