The Oker is a river in Lower Saxony, Germany. It is a tributary of the Aller river and 105 km in length.
The source is located in the Harz mountains, where the river winds through a narrow valley called the Okertal. It then runs northwards through Vienenburg and Wolfenbüttel before entering Braunschweig (Brunswick), the largest city on the banks. Some 30 km north of Brunswick the Oker joins the Aller river.
