Spelga Dam in the Mourne Mountains of County Down, Northern Ireland.
Spelga Dam sits at over 1,200 ft (370 m) above sea level.
The reservoir and dam were built as part of a project that had origins in the idea of supplying water to Belfast, in 1894. The Spelga Reservoir itself was developed between 1953 and 1957.
The Portadown and Banbridge areas receive their water supply from it.
Building started in 1953, and ran into problems. They realised as they poured the heavy concrete foundations that the dam was sinking, it was found that it was as much as 40 metres to the actual bedrock. They had started building on large boulders.[The Dam was designed by the Belfast engineering firm of R. Ferguson and S. McIlveen and construction was undertaken by the Laing Group (now Laing O Rourke).