The River Don (also called Dun in some stretches) is a river in South Yorkshire, England. It rises in the Pennines and flows for eastwards, through the Don Valley, via Penistone, Sheffield, Rotherham, Mexborough, Conisbrough, Doncaster and Stainforth. It originally joined the Trent, but was re-engineered by Cornelius Vermuyden as the Dutch River in the 1620s, and now joins the River Ouse at Goole in the East Riding of Yorkshire. Don Valley is the local UK parliamentary constituency near the Doncaster stretch of the river.