with its source in the upland lake Llyn Aled. The Elwy flows principally eastwards to join the Clwyd, passing through a few villages. At the confluence of the Elwy and the Clwyd, the river becomes tidal and enters a narrow estuary with much wildlife before meeting the Irish Sea at Rhyl.

In 1277, King Edward I sited a castle next to the Clwyd at Rhuddlan.