Barmouth is a seaside town and community in the county of Gwynedd, north-west Wales; it lies on the estuary of the Afon Mawddach and Cardigan Bay. Located in the historic county of Merionethshire, the Welsh form of the name is derived from aber (estuary) and the river's name, Mawddach. The English form of the name is a corruption of the earlier Welsh form Abermawdd. The community includes the villages of Llanaber, Cutiau and Caerdeon.

The Afon Mawddach is a river in Gwynedd, Wales, which has its source in a wide area SH820300 north of Dduallt in Snowdonia. It is 28 miles (45 km) in length, and is much branched; many of the significant tributaries are of a similar size to the main river. The catchment area is bounded to the east by the Aran Fawddwy massif and to the west and north by the Harlech dome which forms a watershed just south of Llyn Trawsfynydd.