The River Irwell is a tributary of the River Mersey in north-west England. It rises at Irwell Springs on Deerplay Moor, approximately 1+1⁄2 miles north of Bacup and flows southwards for 39 mi to meet the Mersey near Irlam. The Irwell marks the boundary between Manchester and Salford, and its lower reaches have been canalised and now form part of the Manche…The River Irwell is a tributary of the River Mersey in north-west England. It rises at Irwell Springs on Deerplay Moor, approximately 1+1⁄2 miles north of Bacup and flows southwards for 39 mi to meet the Mersey near Irlam. The Irwell marks the boundary between Manchester and Salford, and its lower reaches have been canalised and now form part of the Manchester Ship Canal.