Australia Has a Lake the Colour of Bubble Gum

Fly over the south coast of Western Australia and you may spot something that looks like a mistake in the paint box. On Middle Island, the largest island of the Recherche Archipelago, a strip of dark green forest separates the deep blue ocean from a lake that is bright, unmistakable pink. It is called Lake Hillier, and it is pink all year round.

The lake is small: about 600 metres long and 250 metres wide, with a rim of white salt and sand around it. What makes it stranger is that the colour is not a trick of the light. Take a sample of the water in a clear container and it stays pink. Many lakes change colour with the sky or the season. This one simply is pink.

The secret is salt and the life that loves it. Lake Hillier is roughly as salty as the Dead Sea, far too salty for most living things. One that thrives there is a microscopic green alga called Dunaliella salina, which can cope with salt at up to 35 percent, about ten times saltier than seawater. It lives by sunlight, and to shield itself from strong ultraviolet light it makes large amounts of a red pigment, beta-carotene, the same pigment that makes carrots orange.

It does not work alone. Researchers who studied the lake's water found a whole community of salt-loving microbes, including a red bacterium called Salinibacter ruber. Together these tiny residents fill the water with reddish pigments. Seen from above, over the pale sandy bottom of the lake, the red turns into the bubble-gum pink that makes the lake famous.

The lake has been known for a long time. A British expedition charting the coast noted it in January 1802, when the explorers saw so much salt crystallised near its shores that it could have loaded a ship. Later, in the late nineteenth century, someone tried to make a business of harvesting that salt, but the venture was given up after about a year. Today the island is quiet, and most visitors see the lake from a scenic flight out of the town of Esperance.

Pink lakes are not unique to Australia; other salty lakes around the world take on similar shades when the same kinds of microbes bloom. What makes Lake Hillier special is how steady its colour is, and how sharp the contrast looks, pink water, white shore, green trees and blue sea all in one view.

How do we know the colour comes from living things and not from minerals? Scientists sampled the water and identified the organisms in it, from the alga to the salt-loving bacteria, and linked their pigments to the colour. It is a reminder that some of the most striking landscapes on Earth are painted by creatures far too small to see, working away in water most of us would never think of as a home.