The Mersey River rises in Derbyshire and after a course of 70 miles, empties into the Irish Sea. From Stockport, where it is joined by the Tame, it winds westward through Lancashire and Cheshire. The Manchester Ship Canal joins the river near Irlam.
Below Runcorn it widens into a large estuary, on the right bank of which lies the great port of Liverpool. A vehicular tunnel two miles long, built in 1934, connects Liverpool with Birkenhead on the left bank.