| Lough Mourne | |
| Pushpin Map: | Island of Ireland |
| Pushpin Map Alt: | Lough Mourne location in Ireland |
| Pushpin Label Position: | none |
| Pushpin Map Caption: | Location in Ireland |
| Location: | County Donegal |
| Lake Type: | reservoir |
| Outflow: | Mourne Beg River |
| Catchment: | 8.87km2 |
| Basin Countries: | Ireland |
| Length: | 1.7km (01.1miles) |
| Width: | 0.5km (00.3miles) |
| Area: | 0.67km2 |
| Depth: | 3.9m (12.8feet) |
| Max-Depth: | 11.9m (39feet) |
| Elevation: | 168m (551feet) |
Lough Mourne is a freshwater lake in east County Donegal, Ireland, near County Tyrone.
Lough Mourne is located about 9km (06miles) southwest of Ballybofey, near the N15 road. The lake serves as a reservoir for Donegal Town. The Mourne Beg River flows out of the southern end of the lough, while the Burn Daurnett flows out of the north-eastern end of the lough. The Red Burn (also known as the Sruhanderg) flows into the western side of the lough.
Fish species in Lough Mourne include roach, pike, brown trout and the critically endangered European eel. The southwestern shore of Lough Mourne forms part of the Croaghonagh Bog Special Area of Conservation. The site provides supports for a range of wildlife species including important bird species.