Port Hacking, an open youthful tide dominated, drowned valley estuary, is located in southern Sydney, New South Wales, Australia approximately 30 kilometres (19 mi) south of Sydney central business district. Port Hacking has its source in the upper reaches of the Hacking River south of Helensburgh, and several smaller creeks, including South West Arm, Bundeena Creek and The Basin and flows generally to the east before reaching its mouth, the Tasman Sea, south of Cronulla and north–east of Bundeena. Its tidal effect is terminated at the weir at Audley, in the Royal National Park. The lower estuary features a substantial marine delta, which over time has prograded upstream. There is also a substantial fluvial of the Hacking River at Grays Point. The two deltas are separated by a deep basin.