Lake Alexandrina (South Australia)
Lake Alexandrina is the largest of the Lower Lakes
|Primary inflows||Murray, Bremer, Angas, and Finniss Rivers|
|Primary outflows||Murray Mouth|
|Catchment area||1,061,469 square kilometres (409,835 sq mi)|
|Surface area||64,900 hectares (251 sq mi)|
|Average depth||2.8 metres (9.2 ft)|
|Max. depth||6 metres (20 ft)|
|Water volume||1,610 gigalitres (0.39 cu mi)|
|Surface elevation||0.75 metres (2.5 ft)|
Lake Alexandrina is a lake in South Australia adjacent to the coast of the Southern Ocean, about 100 kilometres south-east of Adelaide. It adjoins the smaller Lake Albert; together they are known as the Lower Lakes.
The lake was named after Princess Alexandrina, niece and successor of King William IV of Great Britain and Ireland. When the princess ascended the throne and took the name Queen Victoria there was some talk of changing the name of the lake to Lake Victoria, but the idea was dropped.
Lake Alexandrina is located north of Encounter Bay and east of Fleurieu Peninsula. The Murray River is the major river to flow into Lake Alexandrina. Others include the Bremer, Angas, and Finniss Rivers, all from the eastern side of the southern Mount Lofty Ranges. The lake is shallow and contains a number of islands near the southern end.
The lake empties into the sea near Goolwa (the channel is known as the Murray Mouth), but when the river flow is low the entrance is often blocked by a sand-bar. Originally subjected to tidal and storm inflows of seawater the lake is now maintained as fresh water by a series of barrages across the islands near the Murray Mouth.
Though connected to the ocean historically the fresh and salt water flows mixed very little, with the lake area remaining fresh over 95% of the time with normal river inflow. Salt water inflows from the ocean would result in relatively little mixing of fresh and salt water, either vertically in the water column or laterally across the flow stream. Hindmarsh Island is reputed to be the largest island in the world with salt water on one side and fresh water on the other. Lake Alexandrina is connected by a narrow channel to the smaller Lake Albert to the south-east.
Edward Wilson, visiting the lake in the 1850s described it as follows:"Lake Alexandrina is the finest sheet of fresh water I ever saw. Indeed so formidable did it look, with a stiff wind blowing up quite a sufficient swell to make one seasick, that I could scarcely believe it to be fresh. Such is the fact however. It is forty or fifty miles long by twelve or fifteen wide and the shores around it receded into the dim distance until they become invisible, in the way which we are accustomed only with ideas of salt water. Supplied almost entirely by the Murray, the whole lake retains the muddy tinge of which I have spoken, and this sadly detracts from the otherwise beautiful appearances of this magnificent sheet of water."
In 2008, water levels in Lake Alexandrina and Lake Albert became so low that large quantities of acid sulphate soils threatened to form. The soils on the lake beds are naturally rich in iron sulfides. When exposed to the air, such as may occur in a time of severe drought, the sulfides oxidize, producing sulfuric acid. The barrages now prevent seawater inflows that have prevented this phenomenon in every drought since the last ice age. A weir was proposed near Pomanda Point where the river entered the lake to protect upriver and Adelaide's water supplies should it become necessary to open the barrages, but this plan was dropped by the South Australian government after a campaign by the River, Lakes and Coorong Action Group highlighted the many environmental problems such a weir would cause.
Turtles live in the lake, with lizards and snakes present along the shoreline. Insect species include dragon flies, a range of moths and butterflies and large numbers of beetles (coleoptera). Freshwater fish inhabit the lake, including the introduced European carp. The soils around the lake are relatively low in organic carbon although good barley and vegetable crops may be produced. Non-wetting soils are present along the south eastern bounds of Lake Albert and in areas around Lake Alexandrina.
The lake is a habitat for many species of waterbird, including migratory waders, or shorebirds, which breed in northern Asia and Alaska. Species supported by the lake include the critically endangered orange-bellied parrots, endangered Australasian bitterns, vulnerable fairy terns, as well as over 1% of the world populations of Cape Barren geese, Australian shelducks, great cormorants and sharp-tailed sandpipers.
Protected area status
Lake Alexandrina is part of the wetland complex known as the Coorong and Lakes Alexandrina and Albert Wetland which is listed as a Ramsar site. The wetland is also appears in the non-statutory list known as A Directory of Important Wetlands in Australia.
South Australian government
Lake Alexandrina includes the following protected areas declared under the National Parks and Wildlife Act 1972 - Currency Creek Game Reserve, Mud Islands Game Reserve, Salt Lagoon Islands Conservation Park and Tolderol Game Reserve.
Lake Alexandrina is included within the boundary of the Lakes Alexandrina and Albert Important Bird Area which is an area considered by BirdLife International to be a place of ‘international significance for the conservation of birds and other biodiversity.’
- "Alexandrina, Lake". Place Names of South Australia. State Library of South Australia. Retrieved 2007-01-12.
- Wilson, Edward (1859). Rambles at the antipodes: a series of sketches of Moreton Bay, New Zealand, the Murray River and South Australia and the overland route. With 2 maps; and 12 tinted lithographs, illustrative of Australian life. W.H. Smith. p. 45. Retrieved 2 January 2011.
- "Catalyst - Fire, Flood and Acid Mud". Retrieved 2008-05-07.
- "Important Bird Areas factsheet: Lakes Alexandrina and Albert". BirdLife International. Retrieved 19 January 2015.
- "Coorong and Lakes Alexandrina and Albert Wetland Ramsar site" (PDF). Department of Environment Water and Natural Resources. 28 January 2014. Retrieved 19 January 2015.
- "Australian Wetlands Database - Directory Wetland Information Sheet: The Coorong, Lake Alexandrina & Lake Albert - SA063". Commonwealth of Australia, Department of the Environment. 31 May 2005. Retrieved 19 January 2015.
- "Register of the National Estate (Non-statutory archive), Currency Creek Game Reserve, Laffin Point via North Goolwa, SA, Australia". Commonwealth of Australia (C of A), Department of the Environment. 21 October 1980. Retrieved 10 January 2015.
- "Register of the National Estate (Non-statutory archive), Mud Islands Game Reserve, Lake Alexandrina via Goolwa, SA, Australia". Commonwealth of Australia (C of A), Department of the Environment. 21 October 1980. Retrieved 10 January 2015.
- "Register of the National Estate (Non-statutory archive), Salt Lagoon Conservation Park, Salt Lagoon, Narrung, SA, Australia". Commonwealth of Australia (C of A), Department of the Environment. 21 October 1980. Retrieved 10 January 2015.
- "Register of the National Estate (Non-statutory archive), Tolderol Game Reserve, Langhorne Creek, SA, Australia". Commonwealth of Australia (C of A), Department of the Environment. 21 October 1980. Retrieved 10 January 2015.
- "Sites - Important Bird and Biodiversity Areas (IBAs)". BirdLife International. Retrieved 19 January 2015.