Gajah Mungkur Reservoir, Water reservoir in Wonogiri Regency, Central Java, Indonesia.

Gajah Mungkur Reservoir is a water reservoir in Wonogiri Regency, Central Java, Indonesia. The water surface covers seven subdistricts, retained by a dam that rises 40 meters and runs 830 meters from end to end.

The idea was raised in 1941 by Ir. R.M. Sarsito Mangunkusumo, head of Mangkunegaran public works, but only took shape after a 1975 JICA feasibility study and a design by Nippon Koei. The Ministry of Public Works built the dam itself from 1976 under the Bengawan Solo Project, the last Indonesian reservoir constructed without contractors. Around 41,369 people from 45 villages in six subdistricts were resettled, many to Sumatra. Filling began in July 1981 and President Soeharto inaugurated it on 17 November 1981, at a cost of US$111.056 million.

The name comes from the Gajah Mungkur mountains west of the reservoir, not from any legend. A statue at the Sendang recreation park commemorates the villagers resettled from 51 villages, many of whom transmigrated to Sumatra. Boats circle the water and the shoreline is used for fishing and hang-gliding.

The shoreline areas allow for walking and taking in views across the water, especially in the morning or afternoon. Boats operate on the reservoir and bring visitors to quieter spots where fish are raised.

The reservoir was the last in Indonesia built directly by the Ministry of Public Works, without contractors. Its dam stands near the meeting of the Bengawan Solo and Keduang rivers in Pokohkidul village, Wonogiri. In dry seasons the shrunken water exposes part of the bed, which locals plant with corn.