Afon Ddu (Welsh for black river) is the name of several rivers in Snowdonia in north-west Wales.
One flows from Llyn Cowlyd on the south-eastern edge of the Carneddau range to join the river Conwy, passing Pont Dolgarrog on the B5106 road, just south of the village of Dolgarrog. The gorge cut by the river at this point is popular for gorge walking. Coordinates: 53°10′51″N 3°49′58″W / 53.18083°N 3.83278°W
Another is a tributary of the River Conwy near to its mouth.
A third is a coastal stream entering the sea between Abergwyngregyn and Llanfairfechan.
A fourth is a tributary of the River Dysynni in the northern Dysynni Valley, famed for Craig y Deryn.