South Australia is a state of Australia in the southern central part of the country. It covers some of the most arid parts of the continent and with a total land area of 984 377 km² (380 070 sq mi), it is the fourth largest of Australia's states and territories. It is bordered to the west by Western Australia, to the north by the Northern Territory and Queensland, to the east by Queensland, New South Wales and Victoria, and along the south by the Great Australian Bight and the Southern Ocean. With 1.5 million people, the state comprises less than 10 per cent of the Australian population and ranks fifth in population among the states and territories. The majority of its people reside in the capital city Adelaide, with most of the remainder settled in fertile areas along the south-eastern coast and River Murray.
The state's origins were unique in Australia as a freely-settled, planned British province. Official settlement began on 28 December 1836 when the state was proclaimed at The Old Gum Tree by Governor Hindmarsh. The guiding principle behind settlement was that of systematic colonisation, a theory espoused by Edward Gibbon Wakefield that was later employed by New Zealand. The aim was to establish the province as a centre of civilisation for free immigrants, promising civil liberties and religious tolerance. Although its history is marked by economic hardship, South Australia has remained politically innovative and culturally vibrant. Today, the state is known as a state of festivals, and of fine wine.
Blue Lake is a large lake located in an extinct volcanic caldera in Mount Gambier. It is known as Waawor in the local Aboriginal language. During summer and the surrounding months, the lake takes on a vibrant blue colour, returning to a colder steely-grey colour for winter. The exact cause of this phenomenon is still a matter of conjecture but it is generally considered likely that it revolves around the warming of the surface layers of the lake during the summer months to around 25 degrees celsius, causing calcium carbonate to precipitate out of solution and enabling micro-crystallites of calcium carbonate to form. This results in a scatter of the blue wavelength of sunlight. The movement of planktonic life-forms within the lake during the seasons and during the day may also play a part in the visibility changes.