It's Australia's largest lake — and the world's 18th largest — but not all the time. In fact most of the time it's not a lake at all if you define lake as a landlocked body of water.
It's Lake Eyre — officially known as Kati Thanda-Lake Eyre since December 2012 in recognition of its original Aboriginal name — and it's mostly dry. But when strong rains in the north swell rivers and send cubic kilometres of water thundering through the Outback down to Kati Thanda-Lake Eyre, it does become Australia's occasional and largest inland sea.
Australia's lowest point
At about 15 metres (49 feet) below sea level, Kati Thanda-Lake Eyre occupies the lowest point in the Australian continent.
Located some 700 kilometres (435 miles) north of the South Australia capital of Adelaide and 270 kilometres east of the opal mining town of Coober Pedy, Lake Eyre is a now-you-see-it-now-you-don't wonder of Nature.
When the lake's a lake
The lake fills up so rarely that when it does, birds breed on its shores, fish swim in its waters and yes, the Lake Eyre Yacht Club may hold its once-in-a-blue-moon regatta there.
Of course, the smaller sub-lakes at its margins may retain water but the whole lake area only fills a few times in a hundred years. A part fill of 4 metres may occur once every 10 years and 1.5 metres every three years.
Large numbers of Australians, as well as visitors from overseas, go on sightseeing flights — from Adelaide, Broken Hill or the nearby Outback towns of Lyndhurst and Marree — over the rare occasions there's water in the lake.
And when the lake isn't
Even when the lake's not a lake, there are tours that bring you to the land its traditional owners call Kati Thanda. There are day tours, for instance, from Coober Pedy through Anna Creek and William Creek to Halligan Bay on the western side of Lake Eyre National Park.
Check with South Australia visitor centres for tours to the lake area.
When the lake is dry, it has also been a site for land speed record attempts, such as that of British speed driver Donald Campbell in his Bluebird Proteus CN7 in 1963 and 1964 reaching a record speed of 648.73km/h. That record disappointed Campbell since the car had been designed to reach a maximum speed of 800km/h.
Water and salt
Because of accumulated salt on the lake bed, first there's fresh water in the lake as it fills, then as the salt crust begins to dissolve and evaporation reduces the proportion of fresh water, Kati Thanda-Lake Eyre becomes a salt lake.