The Alster (German pronunciation: [ˈalstɐ] ⓘ) is a right tributary of the Elbe river in Northern Germany.

The source of the Alster is a small bog pool in the Timhagen Brook near Henstedt-Ulzburg, approximately 25 km (16 mi) north of Hamburg.

The small brook makes a couple of curves before entering Hamburg territory at Duvenstedt and Wohldorf-Ohlstedt.

These two lakes and the surrounding parks serve as important recreational areas in the heart of the city.

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.

[2] Hamburg expanded along the shores of the Alster, and several locks were constructed to make the river navigable.

Hamburg's Alster and its lakes and canals are famous for its white swans, cared for out of public funds since the 16th century.

[4] Throughout much of Germany, an Alsterwasser (literally: "Alster's water") is the name for a type of shandy, a concoction of equal parts of beer and lemonade.