Off the southern coast of Western Australia sits a body of water that looks less like a natural lake than a spilled strawberry milkshake. It runs about 600 metres along Middle Island, the largest island of the Recherche Archipelago, and holds a saturated, opaque pink that does not drain away when the water is scooped into a glass. For more than two centuries the color has puzzled the sailors, surveyors and scientists who came across it, and only in recent years have researchers begun to pin down what actually creates the shade.
A pink lake first logged in 1802
European records of the lake reach back to the expedition of the navigator Matthew Flinders, who climbed the island’s highest point in 1802 and noted the strange rose-colored water below. The lake was later named for William Hillier, a member of the crew who died during the voyage. As described by Britannica, the lake is separated from the deep blue of the Southern Ocean by only a narrow rim of sand and a dense fringe of paperbark and eucalyptus, an arrangement that frames the pink water against the sea and makes the contrast especially vivid from the air. Shallow and heavily salted, the lake supported a brief salt-mining operation in the early twentieth century before being left largely undisturbed.
The microbes that tint the water
The color is not a trick of light or a stain from the rock beneath but the product of living things adapted to punishing salt levels. The best-known contributor is a single-celled alga, Dunaliella salina, which flourishes in hypersaline water and manufactures large amounts of beta-carotene, the same orange-red pigment that gives carrots their color. That alga is farmed commercially elsewhere precisely for its beta-carotene, which is sold as a natural food coloring and dietary supplement, so the compound turning the lake pink is the same one found on health-store shelves. Living alongside it is a salt-loving bacterium, Salinibacter ruber, that carries its own reddish pigments. A cross-kingdom genetic survey of the lake published in 2022 in the journal Frontiers in Microbiology found that the water is not ruled by any single organism but by a dense community of bacteria, archaea and algae, many of them extremophiles that thrive where almost nothing else can live.
Why the color survives in a jar
Part of the lake’s mystique comes from a simple observation: a sample of its water keeps its pink tint after being carried away, unlike colored lakes whose appearance depends on depth, angle or the weather overhead. The reason is that the color is carried by pigments locked inside microbes suspended throughout the water and by the salts they live in, rather than by anything reflecting off the lakebed or the sky. The water is intensely saline, in places rivaling the concentrations that make it easy to float in the Dead Sea, and that extreme chemistry is exactly what lets the pigment-rich organisms outcompete everything else. Related pink and rose-colored lakes appear elsewhere in Australia and around the world, and reporting collected by Live Science traces the same broad recipe of salt-tolerant microbes producing rosy pigments across many of them.
Still not a fully settled question
For decades the pink was attributed almost entirely to Dunaliella salina, and that shorthand still appears in many descriptions of the lake. The more recent genetic work complicates the story by showing that the color emerges from a whole consortium of species interacting, with Salinibacter and other pigment producers each adding to the effect. Researchers have not fully quantified how much each organism contributes to the final shade, which is why careful accounts still say that no one is entirely certain why the water is quite so pink. The lake’s isolation compounds the uncertainty. It sits inside a protected nature reserve, is reached mainly by boat or aircraft, and is studied far less often than its fame would suggest.
A protected curiosity, not a swimming hole
Because Middle Island is part of a conservation area, visitors are generally kept from wading into the lake, and most people encounter it through aerial photographs rather than in person. That protection helps preserve the fragile microbial balance responsible for the color, since large-scale disturbance could alter the salt levels and the community of organisms that depend on them. The water itself is not considered dangerous, since the salt rather than any toxin is what defines it, but the lake’s value lies precisely in being left alone. What is clear, after two hundred years of speculation, is that the pink is biological, remarkably stable, and tied to one of the harshest and least accessible little ecosystems in Australia.
This article was produced with the assistance of AI and reviewed by Morning Overview editors prior to publication.
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