Alster

Alster
River
Aerial view of the Alster's two lakes in Hamburg
Country	Germany
States	Schleswig-Holstein, Hamburg
Tributaries
- left	Bredenbek, Ammersbek, Saselbek, Osterbek, Wandse
- right	Tarpenbek, Isebek
Source
- location	Henstedt-Ulzburg
- elevation	31 m (102 ft)
- coordinates	53°45′49.1″N 10°0′17.4″E / 53.763639°N 10.004833°E / 53.763639; 10.004833
Mouth	Elbe
- location	Hamburg
- elevation	4 m (13 ft)
- coordinates	53°32′40″N 9°59′0″E / 53.54444°N 9.98333°E / 53.54444; 9.98333Coordinates: 53°32′40″N 9°59′0″E / 53.54444°N 9.98333°E / 53.54444; 9.98333
Length	56 km (35 mi)
Area	587 km2 (227 sq mi)
Discharge
- average	5.8 m3/s (205 cu ft/s)
Lakes	Außenalster, Binnenalster, Kleine Alster
Map of Alster and canals in Hamburg

The Alster is a right tributary of the Elbe river in Northern Germany. It has its source near Henstedt-Ulzburg, Schleswig-Holstein, flows somewhat southwards through much of the Free and Hanseatic City of Hamburg and joins the Elbe in central Hamburg.

The Alster is Hamburg's second most important river. While the Elbe river is a tidal navigation of international significance and prone to flooding, Alster is a non-tidal, slow-flowing and in some places, seemingly untouched idyll of nature, in other places tamed and landscaped urban space. In the city center, the river forms two lakes, both prominent features in Hamburg's cityscape.

In total, the Alster is 56 km (35 mi) long and has an incline from 31 m to 4 m above sea level. Its drainage basin is about 587 km² (227 sq mi). Left tributaries to the Alster are: Rönne, Alte Alster, Sielbek, Ammersbek, Drosselbek, Bredenbek, Rodenbek, Lohbek, Saselbek, Osterbek, and Wandse (Eilbek); right tributaries to the Alster are: Mühlenau (or Mühlenbach), Diekbek, Mellingbek, Susebek, Tarpenbek, and Isebek.

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 und Wohldorf-Ohlstedt. At that point, the Alster has passed a couple of smaller locks and has been passed by 15 bridges. From here on, Hamburgers use the river for water sports, especially for canoe and kayak trips on the river, or hikes along its shores. At Wellingsbüttel, the Alster runs past Wellingsbüttel Manor. At Ohlsdorf the Alster reaches a weir, approximately at the height of the former Fuhlsbüttel Lock, the last water level regulation before reaching the inner city. From Fuhlsbüttel downstream, the Alster's course, has been straightened on several locations, with old and new river beds occasionally forming parallel canal beds. Between city limits and the inner city's first lake − the Außenalster − the river is crossed by 42 bridges.