Manly Dam Reserve, Protected area in northern Sydney, New South Wales, Australia.

Manly Dam Reserve encompasses 376 hectares of protected natural landscape surrounding a heritage-listed dam and 30-hectare reservoir, featuring diverse ecosystems with over 300 native plant species including endangered Duffy's Forest Ecological Community.

The concrete gravity dam was constructed in 1892 by the NSW Department of Public Works to provide water supply for Manly village, serving as the primary water source for over three decades before being decommissioned in 1933.

After World War I, a committee of ex-servicemen was given charge of the dam's bushland catchment around 1920, making it a war memorial park. In 1995 the area was re-dedicated to service personnel during the "Australia Remembers" celebrations. A 1998 Plan of Management led to a memorial, sculptures and flagpole in the picnic areas, now the focus of annual commemorations.

The reserve surrounds a 30-hectare reservoir within 376 hectares of bushland adjoining Garigal National Park. The dam wall itself lies outside the reserve boundary and is managed by Sydney Water. Tracks pass picnic areas where eastern water dragons, water skinks and lace monitors are often seen; red-bellied black snakes and common brown snakes also occur along the paths.

The dam wall stands outside the reserve boundary and is managed by Sydney Water, not the park authority. In the early 1990s a large enclosed powered propeller was installed on the reservoir side of the wall to stop silt building up against it and to prevent the water stratifying, which limits eutrophication.