| Lough Fern | |
| Pushpin Map: | Island of Ireland |
| Pushpin Map Alt: | Lough Fern location in Ireland |
| Pushpin Label Position: | none |
| Pushpin Map Caption: | Location in Ireland |
| Location: | County Donegal |
| Inflow: | River Leannan |
| Outflow: | River Leannan |
| Catchment: | 206.17km2 |
| Basin Countries: | Ireland |
| Length: | 2.3km (01.4miles) |
| Width: | 0.8km (00.5miles) |
| Area: | 1.81km2 |
| Depth: | 2m (07feet) |
| Max-Depth: | 3m (10feet) |
| Elevation: | 18.7m (61.4feet) |
| Islands: | 2 |
Lough Fern is a freshwater lake in the northwest of Ireland. It is located in north County Donegal near the town of Milford.
Lough Fern is about 2km (01miles) south of Milford, on the R246 road, and 10km (10miles) north of Letterkenny. It measures about 2km (01miles) long and 0.8km (00.5miles) wide. The lake has two islands at its northern end, including one crannog.
Lough Fern is fed mainly by the River Leannan entering at its southern end and also by a stream entering at the northern end. The lake drains eastwards into the continuation of the Leannan, which in turn enters Lough Swilly at Rathmelton.
Fish species in Lough Fern include brown trout, salmon, three-spined stickleback, perch and the critically endangered European eel. Lough Fern is part of the Leannan River Special Area of Conservation.