Pink Lake Hillier in Western Australia.

Lake Hillier is a pink-colored lake on Middle Island, the largest of the islands and islets that make up the Recherche Archipelago, Western Australia. From above the lake appears a solid bubble gum pink. It is such a significant distinguishing feature of the archipelago that air passengers often crane their necks to take a glimpse of it.

The lake is about 600 meters long, and is surrounded by a rim of sand and a dense woodland of paperbark and eucalyptus trees. A narrow strip of sand dunes covered by vegetation separates it to the north from the Southern Ocean.

Unlike other pink lakes in the world like the one in Retba and the salt ponds at San Francisco Bay, the pink color of Lake Hillier has not been decisively proved, although it is speculated that the color could arise from a dye created by the organisms Dunaliella salina and Halobacteria. Another hypothesis is that the pink color is due to red halophilic bacteria in the salt crusts. That the color is not a trick of light can be proved by taking water from the lake in a container – the pink color can be found to be permanent.

One of the first evidence of Middle Island's pink lake dates back to the journals of Matthew Flinders, a British navigator and hydrographer in 1802. Flinders had climbed Middle Island's highest peak (now known as Flinders Peak) to survey the surrounding waters when he came across this remarkable pink lake. Except for a few years when salt extraction was being carried out here, the island and its pink lake has been almost untouched and has since then provide visitors with one of the most amazing view of the world's natural wonder.

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