Rambakan Oya Dam, Embankment dam in Maha Oya, Eastern Province, Sri Lanka.

The Rambakan Oya Dam is an embankment structure built across the Mundeni Aru River in Sri Lanka's Eastern Province. It holds back water in a large reservoir that supplies irrigation and drinking water to several districts in the region.

Archaeological evidence points to construction attempts at this site dating back to the third century BC, ordered by Prince Giri Abaya. The structure reflects an important chapter in Sri Lanka's ancient water management practices.

The Rambakan Oya Slab Inscription, near the old sluice, dates from the 12th to 13th centuries and records that the stone canal was built by Liyana Nayakayan and Kanathkan Vahanse, who lived in the Gal Weta area. The reservoir now supplies drinking water and irrigation to the surrounding districts.

The dam lies in Maha Oya, Ampara District, near where Badulla, Monaragala and Ampara districts meet, and is reached by local roads from Maha Oya town. The reservoir is managed by the Ministry of Irrigation and Water Resources Management, so access to the dam structure itself may be restricted; ask locally before walking along the 1,225 m embankment.

Beside the modern dam, a one-mile earthen bund once linked Gorikanda and Galkanda, built with rip rap; around 250 feet of dressed stone for its twin barrel sluice still lie nearby. A 12th–13th century slab inscription records that Liyana Nayakayan and Kanathkan Vahanse of Gal Weta built the stone canal.