The Upper Harz Water Tunnels (German: Oberharzer Wasserläufe, pronounced [ˌoːbɐhaːɐ̯tsɐ ˈvasɐlɔʏfə]) are part of the Upper Harz Water Regale - a network of reservoirs, ditches, tunnels and other structures in the Harz mountains of central Germany. The German term Wasserlauf refers to the underground element (i.e. the tunnels) of the network of watercourses used in the historic silver mining industry of the Upper Harz. This network of ditches and tunnels was used to supply the mines with headrace waters for their water wheels from the 16th century onwards. In the system of the Upper Harz Water Regale there are over 35 such tunnels with a total length of about 30 km (19 mi).