The River Ceiriog () is an long river in north east Wales. It is a tributary of the River Dee. It rises at an altitude of around on the south east slopes of Moel Fferna in the Berwyn Mountains, and flows through the Ceiriog Valley in Wrexham County Borough. It flows below Chirk Castle and the town of Chirk, where the Chirk Aqueduct carries the Llangollen Canal over the river. The Ceiriog joins the Dee east of the town. In its lower reaches the river forms the border between Wales and Shropshire in England. Home to a Trout fishing club, the river and its valley were described by British prime minister David Lloyd George as a little bit of heaven on earth. As well as being a home to trout the first grayling to be artificially reared in Wales were released into the river in 2009.