Afon Dulyn (English : River Dulyn) 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.
Ceunant Dulyn, or the Dulyn Gorge, has been designated a Site of Special Scientific Interest (SSSI) since 1 January 1961 as a conservation measure to protect the site on account of its wildlife.[1] Its area is 35.66 hectares. Natural Resources Wales is the body responsible for the site.