Oker

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Oker
Confluence of the Oker and Aller near Müden
Origin	Harz Mountains 51°46′42″N 10°29′29″E / 51.77833°N 10.49139°E / 51.77833; 10.49139
Mouth	Aller 52°31′26″N 10°21′39″E / 52.52389°N 10.36083°E / 52.52389; 10.36083Coordinates: 52°31′26″N 10°21′39″E / 52.52389°N 10.36083°E / 52.52389; 10.36083
Basin countries	Germany
Length	105 km (65 mi)
Source elevation	900 meters (2,953 feet)
Basin area	1,800 km² (695 sq mi)

The Oker is a river in Lower Saxony, Germany. It is a left tributary of the Aller river and 105 kilometers (65 mi) in length, running generally northerly.

Okertal

The source is located at the Bruchberg mountain near the town of Altenau within the Harz mountain range. Leaving the Harz, the river winds through a narrow valley called Okertal. It then runs northwards through the Oker district of Goslar, passing the towns of Vienenburg and Wolfenbüttel before entering Brunswick (Braunschweig), the largest city on the banks, where its waters filled the moats of the medieval town walls. The Oker then passes through a culvert underneath the Mittellandkanal and some 30 kilometers (19 mi) farther north of Brunswick joins the Aller river at Müden.

First mentioned as Ovacra in a 781 deed its name may stem from the Slavic term kra meaning ice floe. The Oker has been a border river since medieval times, when it separated the Bishopric of Hildesheim in the west and the Bishopric of Halberstadt in the east, later the border of the Kingdom of Hanover with the Duchy of Brunswick and the Prussian Province of Saxony. A section between Vienenburg and Schladen until 1990 was part of the Inner German border.

Tributaries