WHAT IS THIS? · Australia's bubblegum-pink lake

On an island off the south coast of Western Australia, there is a lake so pink you can spot it on satellite images. Is the colour natural, is it a chemical spill, or what?

The pink lake is named Lake Hillier, and the colour is natural. Lake Hillier is located on Middle Island, an uninhabited nature reserve off the WA south coast, east of Esperance.

The lake’s bright pink colour is due to an unusually high presence of the monocellular microalga Dunaliella salina. The alga produces a carotenoid, a very powerful pigment related to the one that makes carrots orange, tomatoes red, and crustaceans pink.

The small alga uses the carotenoid for the same purpose as green plants use their chlorophyll, to generate energy from sunlight. However, the carotenoid provides another advantage: it protects the alga when the solar radiation becomes too intense.

However, scientists think that Dunaliella salina is not solely responsible. The 600-metre-long lake is some eight times saltier than the ocean, and scientists found some 500 ‘extremophiles’ (creatures that can survive harsh conditions) in its waters, including salt-resistant purple microbes and red-orange bacteria. So these may also be contributing to the year-round pinkness of Lake Hillier.

1 Middle Island and its pink lake were visited by European sailors for the first time in 1802. The leader of the expedition was a Brit, Matthew Flinders, who named the lake Lake Hillier after one of his dead crew members. Back then Australia was still known as New Holland.

2 On several occasions, Lake Hillier’s high salt content has been used for kitchen salt production. There is still a rail track visible from the lake to the coast, one of the only signs of civilisation on the island. During the 1800s, Middle Island also functioned as a base for seal hunters and whalers.

3 Lake Hillier is not the only pink lake. Australia has more than 10 of them. In Senegal, West Africa, Lake Retba also has an extremely high salt content and hosts the Dunaliella salina micro-alga. There is also a pink lake in Europe: Lake Lemuria in SouthEastern Ukraine.