[3] Manly Dam was built in 1892 by the NSW Department of Public Works as a water supply dam for the Manly area, which was progressively called on to supply neighbouring suburbs such as Balgowlah and Seaforth and eventually the coastal strip of the former Warringah Shire, to as far north as Mona Vale.

The dam was constructed by the NSW Department of Public Works for the local council under a special Act of Parliament as part of a complete water supply scheme for Manly.

The concrete dam was designed to hold 310.12 megalitres (68,216×10^3 imp gal) and was upgraded in 1909 with an enlarged by-wash being excavated on the eastern side and the old by-wash built up, thus enabling the top level of the reservoir to be raised and the storage capacity increased to 380 megalitres (84×10^6 imp gal).

By 1928, increasing demand for water had overtaken the dam's capacity and in 1929, it was phased out, with supply for Warringah and Manly being provided by pipeline from the main metropolitan system at Pymble Reservoir.

In 1936, the pumping installation was dismantled, following the commissioning of an amplified connection to the main metropolitan system, the completion of a 10-billion-imperial-gallon (45 GL) reservoir at Rocky Hill and the progressive development of the Upper Nepean Scheme.

During a nine and a half month period up to October 1942, 975 megalitres (34.4×10^6 cu ft) of water were drawn to supplement Sydney's supply.

This technique was considered revolutionary at the time and gained world recognition when a paper was presented by Sydney Water Board engineers to the 14th Congress of the International Commission on Large Dams in Rio de Janeiro in 1982.

[3] Manly Dam was listed on the New South Wales State Heritage Register on 18 November 1999 having satisfied the following criteria.

The dam played an important role as an independent water supply scheme for the northern beaches area of Sydney.

[3] The place is important in demonstrating aesthetic characteristics and/or a high degree of creative or technical achievement in New South Wales.

The dam is an impressive structure, with its relatively thin wall standing between the water body of the reservoir on the west and the void and valley floor on the east.

Manly Dam is of technical significance for its association with the Hydraulics Laboratories in the former water treatment plant and its continuing role in the provision of experimental facilities.