Aldinga Bay is a bay located on the east coast of Gulf St Vincent in South Australia about 40 kilometres (25 miles) south-southwest of Adelaide city centre.

Aldinga Bay lies between Snapper Point[note 1] in the suburb of Aldinga Beach at its northern extremity and the remains of Myponga Jetty[note 2] at Myponga Beach at its southern extremity.

[3][4] The bay has no infrastructure for maritime use apart from access to the beach from the road network to launch and retrieve small boats at specific locations permitted by the local government authority, the City of Onkaparinga.

[6][4] The waters of Aldinga Bay are within the Encounter Marine Park.

The south-eastern part of the Aldinga Reef aquatic reserve is within the bay.