The river rises in Killinure townland, in the boggy ground at the northern base of Ouley Hill (186 metres), and is fed by numerous drainage ditches as it passes through the farmland to the south of the town of Carryduff. From here it passes beside Knockbracken open reservoir and flows north down through a gap in the Castlereagh Hills, renamed Purdy's Burn. It then flows into the Lagan Valley, and joins the River Lagan at Minnowburn.