The Hassel Auxiliary Dam or Hassel Dam (German: Hasselvorsperre or Vorsperre Hassel) is an auxiliary dam or pre-dam on the Rappbode Reservoir in the Harz mountains of central Germany. It is located near Hasselfelde in the state of Saxony-Anhalt and impounds the waters of the Hassel, the eastern of the two headwaters of the Rappbode Reservoir. Together with its auxiliary dams, the reservoir supplies drinking water and is owned by the Saxony-Anhalt Dam Company (Talsperrenbetrieb Sachsen-Anhalt). The purpose of the auxiliary dam is to pre-clean water mechanically and biologically before it flows into the main reservoir.Water can be collected from various heights and diverted to the reservoir.