All the rain that falls on the slopes at either side of the southern half of the Lairig Ghru eventually drains into the River Dee, and the "official" source of the River Dee, the Wells of Dee, is high on Braeriach. However the River Dee (as a named watercourse on maps) starts at the confluence of Allt a' Gharbh choirie and Allt na Lairig Ghru. At this point, near the head of Glen Dee, the main valley turns roughly west towards An Garbh Choire, and the Lairig Ghru track continues northward into the hanging valley as shown in the photograph.
