The suburb of Gymea Bay is 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 suburb of Gymea Bay takes its name from the small bay of the same name on the north side of the Port Hacking estuary (also known as the Port Hacking River). The suburb included only the area of the single peninsula between Gymea Bay and the North West Arm of the Port Hacking River and 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.
In 2008, the NSW Geographical Names Board suggested a much enlarged area for the suburb of Gymea Bay, taking in much of former Gymea and even part of the suburb of Miranda, in which the 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 boundaries remain contentious.
The area is 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 and since the 1990s, the invasions of feral deer from the Royal National Park have begun to negatively affect the ground cover underneath the tree canopy.