Matt Baker and Charlotte Smith head to the UK's longest and highest aqueduct, the Pontcysyllte Aqueduct in north Wales. Built in 1795, it is one of 26 cast iron aqueducts in the UK and part of the country's vast canal and river network. Now, for the first time in two decades, it’s going to be drained as part of a major project by the Canal and River Trust. Matt and Charlotte are on hand to see what it takes to maintain this massive landmark. Charlotte learns about the history of the Pontcysyllte Aqueduct and helps the team start the mega engineering process of draining the canal. She then joins the repair team to see how they fix the thousands of iron railings spanning the aqueduct. Matt helps repair part of a nearby canal bank before discovering the species that call it home.