Llyn Brenig is a reservoir located in Wales, in the heart of the Denbigh Moors, at a height of 1200 feet, on the border between the counties of Conwy and Denbighshire. It is used to manage the flow in the River Dee as part of the River Dee regulation system which is designed to protect the water supply for North West England and north-east Wales, particularly Liverpool and its surrounding area. The northern half is in the community of Nantglyn and the southern half in Cerrigydrudion, with the village of Pentre-Llyn-Cymmer situated to the south of the lake.