The River Dee is a 70-mile (110 km) long river in the United Kingdom. It travels through Wales and England and also forms part of the border between the two countries. The river rises in Snowdonia, Wales, flows east via Chester, England, and discharges to the sea into an estuary between Wales and the Wirral Peninsula in England.
The River Dee has its source on the slopes of Dduallt above Llanuwchllyn in the mountains of Snowdonia in Merioneth, Gwynedd, Wales, and then passes through Bala Lake. The path of the river trends generally east-south-east as it descends off the Ordovician Denbigh Moors, over the man-made Horseshoe Falls and through Llangollen, generally skirting the outcropping Karstic limestone exposures north of Llangollen. East of Llangollen, Thomas Telford's Pontcysyllte Aqueduct, of 1805, carries the Shropshire Union Canal 120-foot (37 m) overhead.