Port Hacking Estuary (Aboriginal Tharawal language: Deeban[1]), an open youthful tide dominated, drowned valley estuary,[3] is located in southern Sydney, New South Wales, Australia[4] approximately 30 kilometres (19 mi) south of Sydney central business district.

The land adjacent to Port Hacking was occupied for many thousands of years by the Tharawal and Eora, both Aboriginal peoples, and their associated clans.

For more than 8,000 years prior to 1840, the Tharawal (or Dharawal) people occupied the catchment area evidenced by hundreds of Aboriginal artefacts, middens, rock carvings and cave paintings.

The southern bank is largely undeveloped land within the Royal National Park, although the small communities of Bundeena and Maianbar are found there.

Port Hacking is a drowned river valley, with a water surface area of 11 square kilometres (4.2 sq mi).

With very little industrial and minor agricultural inputs via the Hacking River, the water quality is categorised as 'extremely good', and the extensive inter-tidal shoals provide opportunity for wading birds.