Port Noarlunga Reef Aquatic Reserve is a marine protected area in the Australian state of South Australia located in waters in Gulf St Vincent adjoining the Adelaide metropolitan area and including part of the Onkaparinga River about 28 kilometres (17 mi) south-west of the state capital of Adelaide.

[4][5][6] As of 2016, the aquatic reserve extents seaward for a distance of about 1.75 kilometres (1.09 miles) from Gulfview Road in the suburb of Christies Beach in the north with its seaward boundary finishing in the south at the shoreline near the west end of Helmsman Terrace in the suburb of Seaford and includes the full extent of the Onkaparinga River from its mouth to the bridge on the South Road in the suburbs of Noarlunga Downs and Seaford Meadows.

[5][7] The aquatic reserve was declared on 30 November 1971 to protect “reef organisms from exploitation and for the conservation of the estuary and swamps of the lower Onkaparinga River, for the purposes of recreation and education.”[1][5] The aquatic reserve is classified as an IUCN Category VI protected area.

[8] In 1994, the South Australian Research and Development Institute installed an “underwater interpretation trail” in order to “raise community awareness of temperate reef environments and marine life.” The trail which covers a distance of 800 metres (2,600 ft) consists of 12 concrete plinths installed on the seabed and each fitted with a plaque providing information about the reef’s sub-tidal flora and fauna.

[3][7] Since 2012, its full extent has been located within the boundaries of the protected area known as the Encounter Marine Park and is fully occupied by four ‘habitat protection zones’ and two ‘sanctuary zones’ including one extending along the coastline from Witton Bluff in the north and Onkaparinga Head in the south.