The inspection team said it could take months rather than weeks to repair the structure
Divers inspecting a Cumbrian bridge closed since flooding hit the county last month say the structure has been severely damaged.
The massive volumes of water which flowed along the River Derwent have left a hole in the structure of Broughton Bridge at Great Broughton.
Cumbria County Council said it was likely to take months rather than weeks to repair.
Inspections at the Gote Bridge in Cockermouth are continuing.
Structural checks below the waterline on both bridges had been delayed while engineers waited for strong river flows to decrease.
Andrew Butler, an area engineer for the council, said: "It's very sad, this bridge is quite severely damaged.
"There is undermining to the abutment on the far side and the first pier is severely undermined for most of its width so substantial works will be required."
The River Leven bridge at Backbarrow has also yet to be checked by divers.
More than 1,300 homes were flooded and hundreds of properties evacuated during the county's unprecedented rainfall on 20 November.
Six bridges collapsed across the county, including Northside Bridge at Workington, where Pc Bill Barker was swept to his death.
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