Mersey (mûrˈzē) [key], river, c.70 mi (110 km) long, formed at Stockport, W England, by the confluence of the Etherow and Goyt rivers. It flows east to the Irish Sea near Liverpool. The estuary of the Mersey, which is 16 mi (26 km) long and c.2 mi (3.2 km) wide, is navigable for oceangoing vessels. Its chief tributaries are the Irwell and Bollin rivers. The Manchester Ship Canal uses the waters of the Mersey. Mersey Tunnel or Queensway, a vehicular tunnel (opened 1934) with a length of 2.3 mi (3.7 km), was the longest subaqueous tunnel in the world; it connects Liverpool and Birkenhead. Kingsway Tunnel (1.5 mi/2.4 km long; opened 1971) connects Liverpool and Wallasey. The Mersey River is of great commercial importance to the cities served by it, especially Liverpool and Manchester. Shipbuilding, milling, and oil refining are important industries along the river.