The Dyke Ditch (German: Dammgraben) is the longest artificial ditch in the Upper Harz in central Germany. Its purpose was to collect surface runoff for the operation of the Upper Harz mining industry from precipitation-heavy regions a long way away (particularly from the Bruchberg and parts of the Brocken massif). It was laid in 1732 and continually extended eastwards until 1827. Its original length was about 25 km; this was successively shortened by water tunnels between 1820 and 1861 to around 19 km. It is a central component of the Upper Harz Water Regale.