Lough Nacung Upper (Irish: Loch na Cuinge Uachtarach, meaning 'upper narrowness lake' or 'upper lake of the isthmus'),[2] also known as Upper Lough Nacung, is a lake in Gweedore, a district in the north-west of County Donegal, Ireland.

[3][4] It connects Lough Dunlewey to Lough Nacung Lower, which drains into the Clady River.

[3][5] Lough Nacung is a Special Area of Conservation.

[6] The name is derived from the Irish cuing, meaning "lake of the isthmus" or "narrow neck of land (as between two lakes)".

[2][4][7] The main fish species are sea trout and salmon.