The Cordeaux Dam is a heritage-listed dam in Cordeaux, New South Wales, Australia. It provides water to the Macarthur and Illawarra regions, the Wollondilly Shire, and metropolitan Sydney. It is one of four dams and weirs in the catchment of the Upper Nepean Scheme. Completed in 1926 under the supervision of Ernest Macartney de Burgh, the dam is owned by Water NSW, an agency of the Government of New South Wales. It was listed on the New South Wales State Heritage Register on 18 November 1999. Structural details The heritage-listed arch dam across the Cordeaux River with an unlined side spillway on the left abutment is high, long and creates a reservoir which holds . Construction began in 1918 and was completed in 1926 at a cost of A£945,000. The wall consists of large sandstone blocks, quarried onsite and cemented together, faced with a combination of bluestone and sandstone concrete. The dam featured a number of improvements in design and construction on the earlier-completed Cataract Dam. These included contraction joints between units of construction placed at intervals of ; inspection galleries at upper and lower levels, together with piping for registering any ground water pressure. The blue metal used in the construction of the dam was supplied from the Government Quarries at Kiama and brought by rail to Douglas Park. From here it was conveyed by aerial ropeway across the Nepean Gorge to an interchange on the eastern side where the material was transferred to a gauge steam tramway to a point adjacent to the dam site. History The Upper Nepean Scheme was commenced in 1880 after it was realised that the Botany Swamps scheme was insufficient to meet Sydney's water supply needs. The Nepean project consisted of the construction of a weir across the Nepean River to divert of the rivers Cataract, Cordeaux, Avon and Nepean, to the Prospect Reservoir. The design and construction of Cordeaux Dam was undertaken by the Water Supply and Sewerage Branch and Harbour and Rivers Branch of the New South Wales Public Works Department. The construction of the dam necessitated the knowledge and experience of a number of engineers employed in the branches at the time including Cecil Darley (NSW Inspecting Engineer in London), Leslie Wade (Principal Engineer, Water Supply and Sewerage Branch), Henry Dare and Ernest M. de Burgh (Supervising Engineers). The successful completion of the dam and its continuation of use as