In 1914, a water reservoir was completed on the Ploučnice River, at the eastern side of Stráž pod Ralskem, called Horka (Horecký Pond). The dyke is 6 m high; the water area is 69.5 hectares. At present, the reservoir is used for recreation and water sports. It offers water skiing - water skis pulled by a boat or hang-skiing. It is possible to take a boat ride or a ride on a water bike.

Locality: at the eastern side of the town.