Lake Alexandrina (South Australia)

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Lake Alexandrina is a lake in the south of the Australian state of South Australia. It is located about 100 km southeast of Adelaide and is connected to the Indian Ocean.

Lake Alexandrina is located north of Encounter Bay and east of the Fleurieu Peninsula. The Murray River is the largest river that flows into the lake. In addition, there is the Bremer River, the Angas River, and the Finniss River. All these rivers rise on the eastern slopes of the southern Mount Lofty Ranges. The lake is shallow and there are many islands at its southwest end.

At the town of Goolwa, Lake Alexandrina is connected to the ocean; this point is called the mouth of the Murray. However, when river flows are low, this connection is closed with a sandbar. In the past, high tides and southwest storms pushed seawater into the lake. Today, however, only fresh water remains in Lake Alexandrina because a series of flood weirs, the Goolwa Barrages, have been built in between the islands at the mouth of the Murray. Thus, the lake requires an annual inflow of at least 1 billion m³ of water to compensate for evaporation losses.

Although the lake was connected to the sea, fresh and salt water almost did not mix; 95% of the time it contained only fresh water. The influx of salt water from the sea resulted in only minor transverse and longitudinal mixing. Hindmarsh Island (east of Goolwa) is considered the largest island in the world with fresh water on one side and salt water on the other. A small channel connects Lake Alexandrina to the smaller Lake Albert on the southeast side.

The lake was named after the future Queen Victoria, niece and successor of King William IV, who was called Princess Alexandrina in her youth. After Victoria's coronation, there were some voices that suggested renaming the lake Lake Victoria, but this idea did not catch on.

In Aboriginal myths, the lake is inhabited by a monster called Muldjewangk.

Lake Alexandrina provides habitat for a number of waterfowl, including some migratory species from the northern hemisphere. Pelicans, black swans and a number of other birds live on the insects, plants and water of the lake. For example, these include wrens, garden fantails, swallows and ravens. Birds of prey, such as eagles and hawks, can often be seen flying over the water and adjacent shoreline areas. Turtles live in the lake, and lizards and snakes can be found along the shore.

Occurring insect species are dragonflies, a number of moths and butterflies and a large number of beetles. There are also freshwater fish in the lake, such as the carp. The soils around the lake are poor in organic carbon compounds, but barley and other cereals grow well there. Dry soils are found on the southeast shores of Lake Albert and in certain areas around Lake Alexandrina.

In 2008, water levels in Lake Alexandrina and Lake Albert dropped to the point where large amounts of sulfuric acid soils formed. Lake-bottom earths are typically rich in natural iron sulfide. When they are exposed to the air supply, as can happen during major droughts, the sulfides are oxidized and sulfuric acid is formed. Today, flood weirs prevent seawater from entering, which has stopped this process in every drought so far since the Ice Age. It has been proposed to build a weir at Pomanda Island to protect drinking water supplies upstream, in case it becomes necessary to open the flood weirs.

The journalist Edward Wilson, who visited the lake in the 1850s, described it as follows:

"Lake Alexandrina is the most beautiful freshwater lake I have ever seen. It really looked so wonderful when a stiff breeze came up, bringing out waves that could make you seasick, so I almost couldn't believe it was a freshwater lake. This, however, is precisely the case. It is forty or fifty miles long, about twelve or fifteen miles wide, and its shores disappeared into the distance until they became altogether invisible, in the way we know only of the sea. The lake is almost wholly fed by the Murray, and so remains the marshy pool of which I have spoken, and this unfortunately detracts from the otherwise magnificent appearances of this wonderful expanse of water."


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