Ottenstein Reservoir, Reservoir in Lower Austria, Austria

Ottenstein Reservoir sits in the Kamptal valley, extending several kilometers along the river course with densely wooded shores. Multiple bays and a peninsula crowned by ruins divide the water surface into distinct sections.

Plans to use the Kamp for power date to before World War I; a 1913 concession lapsed during the war, and interwar and Depression-era attempts failed. In 1943 Siemens-Schuckert drew up a scheme for nine storage plants, three run-of-river plants and a balancing works. After 1945 the state of Lower Austria took up the three most economical projects; concreting began on 14 October 1954, the first machine set ran on 14 October 1956, and Chancellor Julius Raab opened the pumped-storage plant on 6 July 1957. A geological fault zone found during excavation forced the dam 50 m downstream.

The reservoir's name comes from Ottenstein Castle, which stands on a peninsula and can be seen from the water. The fjord-like bays are partly reachable only by (rental) boat, and anglers catch pike, carp, perch, zander, tench and trout. The Lichtenfels ruin also lies on a peninsula overlooking the lake.

A circular trail of roughly 11 kilometers (7 miles) follows the shoreline and provides access to viewpoints and swimming spots. Fishing permits can be arranged through the local forestry office or nearby farms.

The Lichtenfels ruins stand on a peninsula jutting into the lake, visible from the shoreline path. Pike, carp, and zander inhabit different depths of the water, drawing anglers from the surrounding region.