masonry, and some 100,000 tons were carried along an extended railway to the construction site. Although the contractors Holme and King of Liverpool were employed to do much of the preparatory work, the building of the dam was carried out by direct labour, with Merthyr Corporation's surveyor, Thomas F Harvey, acting as resident engineer. Work began in 1896 and finished in 1902. It holds , and with a water level at , it is one of a very small number of artificial lakes built above the contour. The dam has a small tower to the west, and a larger one to the east, below which a tunnel outlet built in Piranesi style sits at the base of the dam. Neuadd House, built as part of the reservoir project in 1896, is just downstream from the dam. An octagonal building at the east side of the Lower Neuadd dam is also a listed structure. The river continues southwards through a steep-sided wooded valley and is crossed by Pont Cwmyfedwen, an early- to mid-19th century single span bridge before it reaches Pentwyn Reservoir, the oldest of the four reservoirs. It was built by the Merthyr Board of Health between 1859 and February 1863, and the consulting engineer for the project was Thomas Hawksley, but despite this, the dam was built over a geological fault, which led to large volumes of leakage. This leakage was one of the main factors that led to the construction of the Lower Neuadd Reservoir. Remedial work was carried out at regular intervals, but never seemed to last for long. Repairs undertaken in 1912/13 reduced the level of leakage from which was sufficient until Pontsticill Reservoir could be built to impound the leaking water. The corporation had obtained the Act of Parliament to authorise it in 1911, and awarded a contract to Sir Robert McAlpine & Sons on 16 June 1913. The contract price of £232,000 included various ancillary work including diverting the roads on both sides of the valley. The top of the earth dam was above the valley floor, and the reservoir was designed to hold , although this was subsequently increased a little by raising the water level by . Completion was delayed by the onset of the First World War, and when work resumed in 1922, the Corporation used direct labour. The Taf Fechan Water Supply Act had been passed in 1921, creating the