The River Irwell (/ˈɜrwɛl/ UR-well) is a 39-mile (63 km) long river which flows through the Irwell Valley in North West England. Its source is at Irwell Springs on Deerplay Moor, approximately 1.5 miles (2.4 km) north of Bacup. It forms the boundary between Manchester and Salford and empties into the River Mersey near Irlam.During the 17th and 18th centuries the Irwell's lower reaches were a trading route that became part of the Mersey and Irwell Navigation. In the 19th century the river's course downstream of Manchester was permanently altered by the construction of the Manchester Ship Canal, which opened in 1896. The canal turned Manchester and Salford into a major sea port and led to the development of Trafford Park, which became the largest industrial estate in Europe. Further changes were made in the 20th and 21st centuries to prevent localised flooding in Manchester and Salford, such as the Anaconda Cut and the River Irwell Flood Defence Scheme.During the Industrial Revolution the river became severely polluted by industrial waste but in the second half of the 20th century, a number of initiatives were implemented to improve its water quality, restock it with fish and create a diverse environment for wildlife. Consequently, stretches of the river flowing through Manchester and Salford have attracted large-scale investment in business and residential developments such as Salford Quays, and other parts of the river have become nationally important wildlife havens. The Irwell is used for recreational activities, such as pleasure cruising, rowing, racing and fishing.