The Great Laxey Wheel in the Isle of Man has been stopped from turning after engineers found a structural problem.
A spokesman for Manx National Heritage (MNH) said an issue with a timber rod was discovered during a routine maintenance check on Friday.
The 72ft (22m) diameter wheel is the largest working waterwheel of its kind in the world.
It is unclear at this stage how long the repairs will take or what the cost will be.
Known as the Lady Isabella, the wheell was built in 1854 to pump water out of the Laxey lead and zinc mines.
Brandon Ellis, Properties Manager for MNH, said engineers had identified a structural issue with a large timber rod which connects to the Wheel’s main crank.
“This has necessitated stopping the wheel to allow further detailed assessment of the damage by structural engineers.”
The Victorian structure has been run as a heritage attraction since 1989 and offers visitors panoramic views across the Laxey Valley.
A £250,000 maintenance project including painting, cleaning and masonry and timber repairs was completed in 2015.
The site remains open to the public.