The River Dee has its source on the slopes of Dduallt above Llanuwchllyn in the mountains of Snowdonia in Meirionydd, Gwynedd, Wales. Between its source and Bala Lake the river is known by its Welsh name, Afon Dyfrdwy. Legend tells that the waters of the river pass through Bala Lake and emerge undiluted and unmixed at the outflow. On leaving Bala the river meets its confluence with Afon Tryweryn and passes through the Bala sluice gates, part of the Dee Regulation System protecting communities further downstream from severe flooding. Skirting the village of Llanfor, the path of the river takes it past Llandderfel and under the Grade II listed Pont Fawr bridge. The river trends generally east-southeast through the Vale of Edeyrnion, shadowed by the B4401 Bala to Cynwyd road. Leaving Gwynedd and entering Denbighshire the Dee flows beneath other historic bridges at Llandrillo and Cynwyd before arriving at the town of Corwen. From here the river passes the Iron Age hillfort of Caer Drewyn and enters the Clwydian Range and Dee Valley AONB. Through its forested valley the course takes it through Carrog, Glyndyfrdwy and Llantysilio, with the Llangollen Railway following the river on its route between Llangollen and Corwen.