Crag Lough is an inland lake at the southern edge of Northumberland National Park, 2.5 mi north of Bardon Mill, and 0.5 mi north of the B6318 Military Road in Northumberland, northern England. At this point Hadrian's Wall is at the top of a line of crags, the Whin Sill, with Crag Lough at the foot of the crags.

Etymology

The etymology of Crag Lough is linked to the Cumbric word luch, meaning 'lake' (c.f. Welsh llwch, Scottish Gaelic loch). The 'Crag' element is probably from a word equivalent to Welsh craig, 'cliff'.