Garden Island is an island in the Australian state of South Australia located about 14 kilometres (8.7 mi) north-west of the capital city of Adelaide in an estuary system within the Adelaide metropolitan area which drains into Gulf St Vincent. It is notable as being a site for a mangrove forest, a landfill, a part of the site for the Multifunction Polis, a ship graveyard and a venue for recreational boating activities. It has enjoyed varying degrees of protected area status since 1973.

Gulf St Vincent, sometimes referred to as St Vincent Gulf, St Vincent's Gulf or Gulf of St Vincent, is the eastern of two large inlets of water on the southern coast of Australia, in the state of South Australia, the other being the larger Spencer Gulf, from which it is separated by Yorke Peninsula. On its eastern side the gulf is bordered by the Adelaide Plains and the Fleurieu Peninsula.