The River Tees rises on Cross Fell, Westmoreland [Map] from where it flows through Cow Green Reservoir, County Durham [Map], past Forest-in-Teesdale, County Durham [Map], over High Force Waterfall, County Durham [Map], under Saur Hill Bridge, County Durham [Map], over Low Force Waterfall, County Durham [Map], Middleton-in-Teesdale, County Durham [Map], Eggleston, County Durham [Map], Barnard Castle, County Durham [Map], Whorlton, County Durham [Map], Winston, County Durham [Map], Piercebridge, County Durham [Map], Darlington, County Durham [Map], Croft-on-Tees, County Durham [Map], Sockburn, County Durham [Map], Low and Over Dinsdale [Map], Yarm [Map], Stockton on Tees [Map] before passing through Middlesborough [Map] after which it joins the North Sea.