Woronora Dam were former coal miners from nearby Helensburgh. Late in 1931 the Unemployment Relief Account released funds to build a weir to provide water to the Sutherland-Cronulla area and four years later, work resumed on the dam itself. Woronora Dam was completed in 1941 at a cost of about 13 million. The dam is the only one of Sydney's water supply dams which is not part of the Upper Nepean/Warragamba/Shoalhaven interconnected system. The dam was built with the objective of supplementing Sydney's water supply whilst the much larger Warragamba Dam was constructed. Six of the cottages were retained for on-site maintenance staff housing while the rest of Woronora township site was turned into picnic and recreational areas. Features and location Woronora Dam is curved in appearance and is a mass gravity dam, remaining in position under its own weight. The dam wall has a height of and a length of . Its lower levels are built of cyclopean masonry - massive sandstone blocks that were quarried on site. The main wall is made from blue metal and gravel concrete and there are two inspection galleries located inside. The dam has a separate, serpentine overflow spillway that discharges floodwater at the rate of through a concrete lined cutting into the river downstream of the dam. In 1988 Woronora Dam was upgraded at a cost of A$2.9 million by a system of wall and foundation drains to meet international dam safety standards. The catchment area together with the facilities at the dam are managed by the Sydney Catchment Authority. While there are no towns in the catchment area, parts of the Princes Highway, Heathcote Road and the Illawarra railway line pass through the area and the urban areas of Sutherland and are nearby. Raw water from Woronora Dam is pumped to the adjacent Woronora Water Filtration Plant. This plant is one of nine in Sydney either operated by Sydney Water or privately owned and operated under contract to Sydney Water. The dam and water filtration plant supply water to the areas south of the Georges River including Sutherland, Helensburgh, Otford, Stanwell Tops, Stanwell Park, Coalcliff, Lucas Heights and Bundeena. The Maritime Operations Division within the Department of Defence use the Woronora Dam reservoir to test its sonar facilities. The testing station is on a pontoon in the middle of the reservoir. The dam can be viewed by the public, and has