|This article may be expanded with text translated from the corresponding article in the German Wikipedia. (June 2012)|
Alster in Hamburg
|- left||Bredenbek, Ammersbek, Saselbek, Osterbek, Wandse|
|- right||Tarpenbek, Isebek|
|- location||Henstedt-Ulzburg, Schleswig-Holstein|
|Length||53 km (33 mi)|
The Alster is a right tributary of the River Elbe in Northern Germany. It has its source near Henstedt-Ulzburg, Schleswig-Holstein, flows roughly southwards and reaches the Elbe in Hamburg. In the centre of Hamburg the Alster has been dammed. The Alster forms two artificial lakes in the city of Hamburg.
The source of the Alster river is a small bog pool in the Timhagen Brook near Henstedt-Ulzburg, approximately 25 km (16 mi) north of Hamburg. It is 56 km (35 mi) long and has an incline from 31 m to 4 m above sea level. The drainage basin is about 587 km2 (227 sq mi).
Hamburg—Germany's second-largest city—is the major landmark for the river. Through ponding the river, the artificial lakes Außenalster (outer Alster) and the smaller Binnenalster (inner Alster), and the surrounding parks serve as an important recreational area in the heart of the city.
Hamburg was founded at the mouth of the Alster river in the 9th century and used it as a port. The water was used to flood the moats of the fortifications. The Alster has been dammed since 1190, originally to power a watermill. In 1235 a further dam was built for a second mill, which changed the shape of the river to be like a lake.
In the 15th and 16th century, an Alster canal was built to connect Hamburg with Lübeck. The canal was about 8 km (5.0 mi) long and built from the Alster to the Beste, a tributary of the Trave river, at Sülfeld. Because of the difficulties in holding water, especially near marsh areas, the 91 km (57 mi) long waterway from Hamburg to Lübeck was navigable from 1529 to 1550 only.
The city of Hamburg expanded along the shores of the Alster river, and several locks were constructed to make the river navigable. Until the 19th century water transport with barges were used up to the town of Kayhude. The barges—transporting building material, fuel, and foods—were staked or hauled.
Rönne, Alte Alster, Sielbek, Ammersbek, Drosselbek, Bredenbek, Rodenbek, Lohbek, Saselbek, Osterbek, and Wandse (Eilbek)
Mühlenau (or Mühlenbach), Diekbek, Mellingbek, Susebek, Tarpenbek, and Isebek