The River Derwent rises at Swains Greave ( above sea level) on the eastern flank of Bleaklow, opposite Howden Moors, and some east of Glossop. It flows through the Upper Derwent Valley, and for most of its first forms the county boundary between Derbyshire, on its west bank, and South Yorkshire, on the east bank. Some into its journey it passes through three consecutive reservoirs: Howden, the highest, Derwent and Ladybower Reservoir. Derwent Reservoir is named after the now-submerged town of Derwent, which was named after the river. Once past Howden Reservoir, both banks of the river are in Derbyshire, and the river remains in the county to its mouth. Howden Reservoir is also fed by the River Westend, whilst Ladybower Reservoir is also fed by the River Ashop. The former confluences of the two tributaries with the Derwent are now submerged below the respective reservoirs.