| Gartan Lough | |
| Pushpin Map: | Island of Ireland |
| Pushpin Map Alt: | Gartan Lough location in Ireland |
| Pushpin Label Position: | none |
| Pushpin Map Caption: | Location in Ireland |
| Location: | County Donegal |
| Inflow: | Bullaba River |
| Outflow: | River Leannan |
| Catchment: | 77.44km2 |
| Basin Countries: | Ireland |
| Length: | 3.7km (02.3miles) |
| Width: | 0.5km (00.3miles) |
| Area: | 2.05km2 |
| Elevation: | 67m (220feet) |
Gartan Lough, also known as Lough Beagh South, is a freshwater lake in the northwest of Ireland. It is located in north County Donegal close to the eastern boundary of Glenveagh National Park.
Gartan Lough is about 15km (09miles) west of Letterkenny. It measures about 4km (02miles) long and 0.5km (00.3miles) wide.
Gartan Lough is fed by the Bullaba River entering at its southern end. The lake drains northeastwards into the River Leannan, which in turn enters Lough Fern.
Fish species in Gartan Lough include Arctic char. Gartan Lough is part of the Leannan River Special Area of Conservation.