The
Afon Mawddach is a
river in
Gwynedd, Wales, which has its source in a wide area north of
Dduallt in
Snowdonia. The river is much branched and 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.