|Location||County Down, Northern Ireland|
|Catchment area||1,340 acres (5.4 km2)|
|Basin countries||United Kingdom|
|Water volume||600×106 imp gal (2,700,000 m3)|
|Surface elevation||~ 1,200 ft (370 m)|
Spelga Reservoir is a reservoir in the townland of Spelga (Irish: Speilgeach) in the Mourne Mountains of County Down, Northern Ireland. It was formed by the Spelga Dam and sits at over 1,200 ft (370 m) above sea level. It has a volume of 2,700,000 cubic metres and a catchment area of 5.423 km².
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 Dam was designed by the Belfast engineering firm of R. Ferguson and S. McIlveen and construction was undertaken by John Laing & Sons.[dead link] Building started in 1953, and ran into problems. As they poured the foundations on the bedrock they found that the dam was sinking, it was found that it was as much as 40 meters to the actual bedrock. A more comprehensive ground investigation showed that they had started building on large boulders: "boulders encountered in the site investigation were thought to be bedrock which was subsequently found to be as much as 40m lower".
In 2018, a heatwave and dry weather caused the water supply to drop, exposing what lies on the reservoir bed, an old road that usually sits well below the waterline.
- "Newry & Mourne - The pet lamb". Newry Democrat (online archives). April 2006. Archived from the original on 22 June 2011. Retrieved 23 September 2008.
- Ritchie, p. 126
- Not known, Simon. "Spelga Dam and Reservoir". Retrieved 14 September 2012.
- Tedd, Paul. "Conference papers of the British Dam Society". BritishDams.org. Retrieved 14 September 2012.
- Mourne Mountains.com
- McDowell, Iain (2018-07-11). "Heatwave uncovers submerged Mourne history". BBC News. Retrieved 2018-07-12.
- Ritchie, Berry (1997). The Good Builder: The John Laing Story. James & James.