By 1928 it was realised that Manly Dam had reached its limits and all future expansion would rely on the main metropolitan system.

[6]: 82  Briefly in 1942 after a period of drought, pumps were reinstalled and Manly Dam was brought back into service for nearly 10 months.

The dam wall is listed on the New South Wales State Heritage Register,[3] however it is outside the boundary of the reserve and its management remains the responsibility of Sydney Water.

The 1998 Plan of Management allowed for the development of a war memorial, sculptures and flagpole located in the Park's picnic areas.

The venue is valued by the community for these memorial services; the peaceful nature of the Park adding to its commemorative roles.

[9] The diverse range of plant communities in the Manly Dam Reserve provide a home to a wide variety of native wildlife.

The Park also provides an important refuge for many species such as wrens and thornbills which are becoming increasingly rare in urban bushland areas.

Manly Dam Reserve is also home to the threatened Red-crowned Toadlet which is associated with the rocky ridges and drainages of the Hawkesbury Sandstone formation.

Young Bass fingerlings are now regularly stocked into the dam by the NSW Department of Primary Industries to cater for recreational fishermen.

Manly Dam Reserve is also home to a wide variety of terrestrial and aquatic invertebrates and provides an ideal location for school, university and community groups to study them.

[11][12] In 1999 the local community mounted a vigil and blockade to try and stop the contentious "Ardel" housing development from proceeding at Allambie Heights in the upper catchment (now called Maddison Way).

The attendees included Peter Garrett, Tony Abbott, Cliff Lyons, Craig Riddington and Guy Leech.

[17] Concerned residents and members of the wider community objected to the proposal on several grounds: namely there being a significant fire and evacuation risk for the proposed increase in student numbers; parking and traffic issues in small residential streets; and the loss of significant areas of native bushland belonging to the Manly Dam Reserve and adjacent Council Land – home to a variety of protected and threatened native fauna and flora.