The one which inspired the Hungarian composer Oscar Fetrás to compose the popular Viennese-style waltz “Mondnacht auf der Alster”; sometimes mistranslated to English as “Moonlight on the Alster,” the river Alster actually shoots out of right side of River Elbe in Northern Germany. The river basin was also an important model for the design of the Charles River basin, constructed in the early 20th century.
Having its source near Henstedt-Ulzburg, Schleswig-Holstein, it flows roughly southwards and reaches the Elbe in Hamburg forming two artificial lakes in the city of Hamburg- outer Alster and the smaller (inner Alster). The artificial lakes and the surrounding parks are an important recreational area in the heart of the city Hamburg, the second largest city of Germany.
Hamburg was founded at the mouth of the Alster in the 9th century and used it as a port. The water was used to flood the moats of the fortifications. The Alster was 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. 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. With the course of time, Hamburg flourished along the shores of the Alster, 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.
The Alster Touristik GmbH (ATG), a subsidiary of the Hamburger Hochbahn, provides public and touristic transport on the Alster 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 left tributaries of this beautiful river include Rönne, Alte Alster, Sielbek, Ammersbek, Drosselbek, Bredenbek, Rodenbek, Lohbek, Saselbek, Osterbek, and Wandse (Eilbek). Its right side takes pride in holding tributaries like Mühlenau (or Mühlenbach), Diekbek, Mellingbek, Susebek, Tarpenbek, and Isebek.