The locality and suburb of Gymea Bay are located in southern Sydney, in the state of New South Wales, Australia. Gymea Bay is 27 kilometres (17 mi) south of the Sydney central business district, in the local government area of the Sutherland Shire. The postcode is 2227, which it shares with the adjacent suburb of Gymea. The Gymea Bay locality takes its name from the adjoining Gymea Bay, a small bay on the north side of the Port Hacking estuary).

The locality included only the single peninsula between Gymea Bay and the North West Arm of the Port Hacking River, bounded by Coonong Creek on the north and, on the west, by an unnamed creek flowing south of Gymea Bay Road between Barraran Street and Coonong Road. Gymea Bay became a locality within the suburb of Gymea. Early street directories show the locality of Gymea Bay as part of the suburb of Gymea. In 2008, the NSW Geographical Names Board suggested a much enlarged area for a suburb of Gymea Bay, taking in much of former Gymea and even part of the suburb of Miranda which are separated from the locality of Gymea Bay and its settlement by a deep valley with no roads. This suggested suburb’s extremities are defined by Forest Road on the northeast, Avenel Road on the north, Dents Creek on the west, and the waters of North West Arm and the bay itself to the south. These suggested boundaries remain contentious as the proposal to the NSW Geographical Names Board was made without the required community consultation.^{[citation needed]}

The locality was characterised by large amounts of verdant bushland. However, since the 1980s, increased subdivision with smaller lots, larger houses and increased motor vehicle ownership has decreased the number of large trees. Despite Tree Preservation Orders and Council Greenweb and Greenweb Support planning zones, much of the treescape has been lost. Since the 1990s, the invasions of feral deer from the Royal National Park have begun to negatively affect shrub and ground cover and regrowth of trees.