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Afon Dulyn (Welsh : Black Lake river) is the outflow from Llyn Dulyn, a lake in the Carneddau mountains in north-west Wales. It is a tributary of the river Conwy.
Just below Afon Dulyn the river is joined by Afon Melynllyn, a small river flowing from neighbouring Llyn Melynllyn.
The river does not carry a great deal of water because water is transferred from Llyn Dulyn to the reservoirs of Llyn Eigiau and Llyn Cowlyd.
Coordinates: 53°12′12″N 3°50′08″W / 53.20326°N 3.83552°W