River Derg

River Derg
River Derg and the Ardstraw Bridge
EtymologyFrom Lough Derg, 'red lake'
Native nameAbhainn na Deirge (Irish)
Location
CountryRepublic of Ireland, Northern Ireland
Physical characteristics
Source 
  locationLough Derg, County Donegal, Republic of Ireland
  elevation138 metres (453 ft)
MouthRiver Mourne
  coordinates
54°44′16″N 7°25′49″W / 54.7378°N 7.4304°W / 54.7378; -7.4304
Length45 km (28 mi)
Basin size440 square kilometres (170 sq mi)
Discharge 
  average16.2 m3/s (570 cu ft/s)

The River Derg is a small river in Ireland. The river has its source in Lough Derg, in County Donegal, Republic of Ireland, and it flows into County Tyrone, Northern Ireland, east through Castlederg to join with the River Strule to form the River Mourne. The upper reaches of the catchment are characterised by peatland, while the lower reaches flow predominantly through farmland. The River Derg's length is 28 miles (45 km).

The River Derg is known for its salmon, grilse and sea trout.