The river forms at the confluence of Lingmell Beck and Mosedale Beck on Wasdale Head, which is on the north-western side of Scafell Pike. On its short journey to the coast, the Irt is crossed by the Cumbria Coastal Way long distance footpath, at Drigg Holme packhorse bridge. The Irt flows through the Drigg Dunes and Irt Estuary Nature Reserve before joining the River Esk and River Mite at Ravenglass. The river is tidal up until the railway bridge that carries the Cumbrian Coast Line just south of Drigg railway station.