Oldau barrage, Hydroelectric power station and barrage in Hambühren and Winsen an der Aller, Germany.

The Oldau barrage spans the Aller River, integrating a power generation facility with water control mechanisms and a lock in a single structure. Its design reflects early 20th-century engineering with heavy concrete and steel components built to last.

The weir and lock were built from 1909 to 1918 as part of the canalisation of the Aller between the Leine mouth and Celle, decided by the Prussian state government in 1908. The hydroelectric plant followed: construction began in 1910 and it went into operation in 1911 with 300 kW. The city of Celle sold it to PreussenElektra in 1926; it was shut down in 1972 and saved from demolition in 1974 as a technical monument. Since 1982 its three Francis turbines have run again.

The power station's three Francis shaft turbines, set 30 cm apart in height to work at changing water levels, drive the generator through bell-shaped wooden cog wheels. The plant was saved from demolition in 1974 and declared a technical monument; since 1982 it has generated again, automated and remotely monitored.

The lock chamber is 159 m long and 10 m wide, with a maximum fall of 3.18 m; craft up to 55 m long, 6.60 m wide and 650 t are admitted. Since 1969 only sport and passenger boats use it. The weir and lock are run by the Wasserstraßen- und Schifffahrtsamt Verden.

The three Francis shaft turbines restarted in 1982, each offset 30 cm in height so they can work at changing water levels. They sit in series and drive the horizontal generator shaft through bell-shaped wooden cogwheels, with a head of 4.0 m.