the aire starts malham tarn and becomes a subterranean stream at 'water sinks' about one mile (1.6 km) before the top of malham cove, it then flows underground to aire head, just below malham, in north yorkshire, and then flows through gargrave and skipton. after cononley, the river enters west yorkshire where it passes through the former industrial areas of keighley, bingley, saltaire and shipley. it then passes through leeds and on to swillington and woodlesford. at castleford is the confluence of the aire and calder; just downstream of the confluence was the ford where the ancient british road, used by the romans, crossed on its way north to york. the river re-enters north yorkshire near knottingley and in its lower reaches forms part of the boundary between north yorkshire and the east riding of yorkshire.