Lough Inagh is fed from several mountain streams in the area, but most importantly from the Gleninagh River that starts high up in the Gleninagh Valley on the slopes of Benbaun and Bencollaghduff, and the Tooreennacoona River. After flowing into Lough Inagh, the river flows into Derryclare Lough, and then into Ballynahinch Lake, where it eventually joins the Owenmore River where is flows into Bertraghboy Bay.