catchment area in being relatively untouched bushland in close proximity to a major urban area has a high potential for further research into natural ecosystems. The place possesses uncommon, rare or endangered aspects of the cultural or natural history of New South Wales. The construction technique of mass concrete in the upper sections of the dam wall is a first in New South Wales in dam construction on this scale. It was a technique that came to be exemplified in the construction of the Captain Cook Graving Dock and Warragamba Dam. The size of the dam is unusual given the primary reason behind its construction was the supply of the suburban areas south of the Georges River. Other comparable sized dams are located in the adjoining Metropolitan Catchment which service the greater metropolitan area of Sydney. The design of the spillway weir with its zig zag wall and diversion channels is likely to be unique in New South Wales for the time of construction. The use of a welded mild steel pipeline (the majority of the length of the pipeline is outside the scope of this report) to delivery the water to Penshurst is a first in New South Wales. The Dam is one of two extant dams in New South Wales that incorporate extensive Inter War Stripped Classical architectural detailing in the crest wall and superstructures of the valve and crest house. The crest and valve houses and inlet works retain original ironwork which represent a substantial repository of water supply delivery technology for the era. The place is important in demonstrating the principal characteristics of a class of cultural or natural places/environments in New South Wales. Woronora Dam is representative of a type of gravity dam constructed in New South Wales by the Water Supply and Sewerage Branch of the NSW Public Works Department and Water Board during the first half of the twentieth century. Key representative attributes of the Dam's design and construction include the use of cyclopean masonry bedded in sandstone concrete in the lower section of wall, use of blue metal concrete in the wall facings, use of a spillway set way from the gravity wall, valve and crest houses attractively designed and finished to a high standard, the use of an array of upstream intakes to regulate the quality of water supply, the internal inspection gallery, the foundation drainage system, the contraction joints, and