THE Pontcysyllte Aqueduct - a World Heritage Site - has been receiving a major health check.

Carried out once every 20 years, engineers from national waterways charity Canal & River Trust have completely emptied Pontcysyllte Aqueduct of water to check that the 307m-long structure, built to carry the Llangollen Canal across the Dee Valley 38m below, is in good working order.

Pontcysyllte Aqueduct, nicknamed the ‘stream in the sky’ was built in 1805 by pioneering canal engineer Thomas Telford, and was granted World Heritage Status in 2009.

While the aqueduct is inspected regularly from the towpath, completely emptying the water is allowing the engineers to inspect areas that are normally hidden.

Denbighshire Free Press: The canal along the Pontcysyllte Aqueduct has been completely drainedThe canal along the Pontcysyllte Aqueduct has been completely drained (Image: Newsquest)

Uniquely, this includes looking at the underside of the towpath, as well as the caulking of still water-tight joints along the cast iron trough - which were sealed over two centuries ago with Welsh flannel dipped in boiling sugar!

The inspection is part of a wider maintenance programme for the aqueduct.

Since Christmas, a team from the Canal & River Trust has been working alongside specialist blacksmiths to carry out routine maintenance of the parapets.

Emptying the aqueduct has taken a lot of planning and has involved the Canal & River Trust working with United Utilities to put a bypass in place to continue supplying water from the River Dee.

The inspection and maintenance has been taking place over the winter months when fewer boats are using the canal network, with the aqueduct planned to be reopened upon the outcome of a successful inspection by March 15.

Sally Boddy, Canal & River Trust engineer, said: “It’s the engineer's job to be the voice of the aqueduct, to spot any things that might be causing it damage or may need fixing in years ahead.

"Draining Pontcysyllte Aqueduct for inspection helps us to make sure it is in good condition and to plan any future works that will need doing.

Denbighshire Free Press: Pontcysyllte AqueductPontcysyllte Aqueduct (Image: Newsquest)

“It’s a privilege to work on such an iconic structure and see the handiwork of the canal engineers who built it over two centuries ago.

"The work we are carrying out today is part of that great legacy and will help Pontcysyllte continue to stand strong. 

"As the custodians of an incredible portfolio of aqueducts, locks and bridges – the third largest collection of listed structures in the country – we are determined to keep canals alive and preserve this rich heritage.”

The Pontcysyllte Aqueduct will reopen to the public on March 15.