Two major Scottish canals re-opened after decades of dereliction at a cost of £80 million could revert to a “stagnant ditch” because of lack of maintenance, boaters fear.
Three bridges that open to let boats through are out of action on the Forth & Clyde Canal because of safety concerns.
Scottish Canals has admitted it has insufficient funds to fully repair them.
The canals, which were re-opened in 2001, attract millions of visitors a year.
However, the Forth & Clyde, between Grangemouth and Bowling, was closed to through traffic in January because of “unsafe” bridges at Twechar and Bonnybridge.
Operating times on both canals have also been reduced, which the Inland Waterways Association said will have a “significant” impact on the hire boat trade.
The group has called for the bridges to be repaired “as a matter of urgency” because it said Scottish Canals has a statutory requirement to keep the waterways open.
The moves have effectively closed the canals to through traffic and hampered the ability of boats to get to and from moorings.
Vessel owners are also worried that severely reduced traffic flows will accelerate silting up of the waterways and make them unnavigable.
A bridge at Knightswood in Glasgow has now also been shut for “safety reasons”.
The cost of replacing swing bridges had been a factor in the canal’s closure in 1963.
Pat Bowie, chair of the Keep Canals Alive group, launched in January to campaign for the threatened canals, said: “It used to be all about the regeneration of canals, but degeneration is now kicking in – we are going back to where we were before 2000.”
Bowie, who is also general manager of the Re-union Canal Boats charity, said: “Without boat movement, the canals will soon silt up.
“You also need that ‘floating wallpaper’ to make them attractive to visitors. How soon before they become a stagnant ditch again? They could just become a car park for boats.”
John Bell, who described himself as a “scunnered boater”, said the cutbacks meant he could only move his vessel from Bowling on four rather than the previous seven days a week.
He said: “Scottish Canals is not interested in boats moving on the canal, and with the canal being closed it is giving them an excuse to reduce services even more.”
The Leamington lift bridge in Edinburgh is now operating only five days a week.
Graeme Harvey, founder of the Linlithgow Union Canal Society, said: “It will cause problems for many boats, as there are limited spaces available in the basin to the west of the bridge and anyone managing to get into Edinburgh Quay could be trapped.”
Scottish Canals said detailed investigations of the three shut bridges were planned within weeks “to determine the scale of repairs required and allow us to work up technical solutions.”
Its spokesperson said: “We are confident we will be able to implement a short-term fix to allow occasional operation of the bridges while we work to source funding necessary for long-term repairs.
“At Bonnybridge, we will explore an approach that will either allow the bridge to open on a one-off basis or on very rare occasions.
It is unlikely we will find a solution that allows normal use until additional funds are available.
“However, these works will ensure any boat owner who is currently affected can move to a different location should they wish to do so.”
It is hoped a short-term repair at Twechar “may allow us to safely operate the bridge for this season on a limited basis.
“With 250-year-old assets and a repair backlog in the region of £70m, it’s clear we need considerable additional investment in the infrastructure.”
This year, Scottish Canals will receive £11.6m Scottish Government funding.