A large reservoir built to supply Cardiff with water. Authorised under Cardiff Corporation Act of 1884, (designated Reservoir No.2), work commenced with the cutting of the first sod on 4 May 1886. The first contractor was William Jones of Neath but John Mackay of Newport took over in March 1889. Mackay was released from his contract in June 1891 and the works were completed using direct labour, being inaugurated on 14 September 1892. The capacity was 323 million gallons and the top water level 1073ft. (327m) OD. The dam (SN99621352 - SN99711544, situated at the southern end of the reservoir, is a clay core faced with local stone, although the weir and the steps of the overflow channel are of Cornish granite. Temporary workshops and workforce accommodation were erected to the SE of the dam, and on completion of the project, were moved to the Beacons Reservoir site. A standard gauge railway was constructed from Cefn Coed station on the Brecon and Merthyr Rly., along the W bank of the Taff Fawr. It was opened in 1886 and was extended to the Beacons Reservoir in 1893. It was dismantled in 1897.
D.J.Percival, RCAHMW, 09 August 2006.