has aesthetic, historical, architectural, archaeological, scientific and social significance for future generations, as well as for the present community of NSW. The dam and grounds are recognised by the Heritage Council of NSW as a place which is of significance to NSW in relation to its historical, scientific, cultural, social, archeological, natural and aesthetic values. The place has potential to yield information that will contribute to an understanding of the cultural or natural history of New South Wales. The cyclopean masonry of the dam is an excellent late example of this type of gravity dam construction in the Inter War era incorporating inspection galleries, contraction joints, and ground surface drainage system which demonstrate the principal characteristics of this technology at this time. Terraces and platforms adjoining the dam abutments demarcate the location of plant and equipment used in the construction of the dam, in particular the location of the cableway headtowers, the railway terraces and concrete mixing plant platform. The hillside near the upper picnic area was the site of the original construction township and retains an intact road formation, kerbing and guttering and tennis courts from that era. The integrity is such that collectively these features may potentially provide further insight into the lifestyles of the employees that constructed the dam. The place possesses uncommon, rare or endangered aspects of the cultural or natural history of New South Wales. The wall of the Nepean Dam is the highest of all the dams constructed in the Upper Nepean Catchment Area. Nepean Dam is one of three dams in NSW which incorporate extensive Inter War Stripped Classical architectural detailing. The crest and valve houses and inlet works retain original ironwork which represent a substantial repository of water supply delivery technology of the era. The use of an electronic lift in the wall (albeit now decommissioned) is a first for NSW. The completion of the dam necessitated the construction of a standard gauge (1835mm) railway line from Bargo which is unique in context of dam construction in NSW. The extent of foresight in planning the execution and design of the construction township is likely to be a first ion NSW in regard to dam construction, setting a practice which was further developed at Woronora Dam, and came to be exemplified at Warragamba Dam. The remnant platforms and terraces of the construction area are the largest in scale and most intact in regard