The Spencer Gulf is the westernmost and larger of two large inlets (the other being Gulf St Vincent) on the southern coast of Australia, in the state of South Australia, facing the Great Australian Bight. It spans from the Cape Catastrophe and Eyre Peninsula in the west to Cape Spencer and Yorke Peninsula in the east.

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Spencer Gulf
Location of Spencer Gulf in Australia
Spencer Gulf Show map of South Australia Spencer Gulf Show map of Australia
Location	South Australia
Coordinates	34°25′S 136°45′E
Type	Gulf
Part of	Great Australian Bight
Basin countries	Australia

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The largest towns on the gulf are Port Lincoln, Whyalla, Port Pirie, and Port Augusta. Smaller towns on the gulf include Tumby Bay, Port Neill, Arno Bay, Cowell, Port Germein, Port Broughton, Wallaroo, Port Hughes, Port Victoria, Port Rickaby, Point Turton, and Corny Point.

The first recorded exploration of the gulf was that of Matthew Flinders in February 1802. Flinders navigated inland from the present location of Port Augusta to within 44–39 km (27–24 mi) of the termination of the water body.^[1]

The gulf was named Spencer's Gulph by Flinders on 20 March 1802, after George John Spencer, the 2nd Earl Spencer.^[2] The Baudin expedition visited the gulf after Flinders with Nicholas Baudin giving it the name Golfe Bonaparte and Louis de Freycinet using the name Golfe de la Melomanie on the expedition's published charts.^[3]

By the 1830s, the natural harbour of Port Lincoln had become the site of an unofficial settlement, due in part to its convenience as a base for whaling vessels – which had long operated in the Great Australian Bight. Prior to the selection of Adelaide, some consideration was given to Port Lincoln as the potential site of a capital city.^{[citation needed]}

The Gulf is 77 km (48 mi) wide at its mouth (from Cape Catastrophe to Cape Spencer) and 320 km (200 mi) long (from its mouth to Port Augusta). The western shore of the gulf is the Eyre Peninsula, while the eastern side is the Yorke Peninsula, which separates it from the smaller Gulf St Vincent. Its entrance was defined by Matthew Flinders in 1802 as a line from Cape Catastrophe on Eyre Peninsula to Cape Spencer on Yorke Peninsula.^[2] At the time of Flinders' exploration the gulf was noted to extend 298 km (185 mi) inland from a point near the Port Augusta crossing.^[1] This so-called extension of the gulf consists of a land depression and occasional watercourse known as the Pirie–Torrens corridor, and the inland waterbody Lake Torrens.

The northern end of the gulf is spanned by the Joy Baluch AM Bridge between Port Augusta and Port Augusta West and further north by Yorkey Crossing.

Informal names for subdivisions of the gulf waters are sometimes used. "Northern Spencer Gulf" refers to waters north of Wallaroo and Arno Bay, while "Southern Spencer Gulf" refers to waters south of that line, extending to the mouth of the gulf. "Upper Spencer Gulf" includes the waters north of Port Pirie, and includes the three towns sometimes referred to as the Iron Triangle: Whyalla, Port Augusta and Port Pirie. Its boundary lacks precise definition.

The land surrounding the gulf, consisting of the Eyre and Yorke Peninsulas, is the Eyre Yorke Block bioregion. This was originally wooded shrubland but has now mainly been cleared for agriculture. The arid Gawler bioregion extends to the Spencer Gulf on the north-west. Many of South Australia's iconic marine species can be found on the shores and in the waters of Spencer Gulf.

Spencer Gulf contains a number of inshore and offshore islands. These include (from north to south):

• Curlew Island (south of Port Augusta)
• Weeroona Island (north of Port Pirie)
• Shag Island (north of Port Broughton)
• Entrance Island (near Cowell)
• Bird Islands (near Wallaroo)
• Lipson Island (north of Tumby Bay)
• Tumby Island (south of Tumby Bay)
• Wardang Island & the Goose Island group (near Port Victoria)
• The Sir Joseph Banks Group (offshore from Tumby Bay)
• Louth Island & Rabbit Island (in Louth Bay)^[12]
• Boston Island (in Boston Bay)^[12]
• Grantham Island and Bicker Isles (in Proper Bay)^[12]
• Donington Island, Carcase Rock, Owen Island, Taylor Island, Grindal Island, Little Island, Lewis Island, Smith Island, Hopkins Island and Thistle Island (east of the Jussieu Peninsula).^[12]
• Middle Island, South Island and Royston Island (in Pondalowie Bay)
• Gambier Islands including Wedge Island (in the mouth of Spencer Gulf)

Due to its proximity to many identified mineral deposits in South Australia's Far North, Eyre Peninsula and Braemar regions, there are multiple new port and harbour developments proposed for the region.

These include new or expanded facilities at (from north to south):

• Port Bonython - Port Bonython Bulk Commodities Export Facility - Spencer Gulf Port Link (proposed 2012)^[13]
• Port Playford - Iron ore transshipment port proposed to be constructed on the site of the former Playford A Power Station, south of Port Augusta
• Whyalla - Inner harbour expansion - Arrium (completed 2013)^[14]
• Port Pirie - Possible expansion for trans-shipment of iron ore from the Braemar region (concept stage)^[15]
• Lucky Bay - Lucky Bay Common User Export Facility (harbour expansion) - SeaSA (proposed 2013, construction commenced 2014)^[16]
• Myponie Point - Possible port location for Braemar region mineral exports (concept stage)^[17]
• Cape Hardy - Iron Road Limited (proposed 2013)^[18]
• Lipson Cove - Port Spencer (formerly known as Sheep Hill) - Centrex Metals (proposed 2011)^[19] The port could be completed in 2023.^[20]

In 2022, the government of South Australia announced the Northern Water Supply Project, which as of 2023, is considering a business case for establishing a large seawater desalination plant in the upper Spencer Gulf. If constructed, water will be supplied for use to the Olympic Dam and Carapateena copper mines in the state's far north.^[21] It is also intended to supply water for a prospective hydrogen export industry. An environmental impact statement for the project is anticipated mid-2024.^[22]

As of 2016^[update], one reverse osmosis and one thermal seawater desalination plant draw water from Spencer Gulf. Several others are planned. All currently or will produce water primarily or exclusively for industrial use. They are:

The Spencer Gulf region, its wildlife and its development are the subjects of a documentary film in production (as of 2020) entitled Cuttlefish Country.^[34]

• The harbor of Port Broughton on the Eastern shore of Spencer Gulf
• Spencer Gulf seen from one of NASA's Satellites
• Moonta Bay Jetty on the Eastern shore of Spencer Gulf