Howden and Derwent Reservoirs in the upper valley were both completed in 1916 to supply the cities of Sheffield, Nottingham, Derby, and Leicester. The adjacent Ladybower Reservoir was completed in 1945 to cover increasing demand. Treated water from these reservoirs flows down the Derwent Valley Aqueduct parallel to the river. The river also indirectly supplies Carsington Reservoir, with the water taken from the river by a pumping station at Ambergate in times of high flow. When flows are low, water is released back into the river via the same route of tunnels and aqueducts, thus allowing greater abstraction rates downstream at Little Eaton in the drier summer months. Today all these reservoirs are managed by Severn Trent Water.