From the air, it looks almost fake: a bright, bubble-gum pink lake sitting right beside the deep blue Southern Ocean, separated only by a thin strip of sand and bush. Lake Hillier, on Middle Island off the south coast of Western Australia, is one of the most photographed natural sights in the country. So why is Lake Hillier pink? Most websites still give a one-word answer, algae, but when scientists finally tested the lake’s DNA, they found that answer was only part of the picture.
A rose-coloured lake on a remote island
Lake Hillier sits on Middle Island, the largest island in the Recherche Archipelago, off the coast near Esperance. The first European to record it was the navigator Matthew Flinders, who climbed the island’s highest peak in January 1802 and noted “a small lake of a rose colour”, as Australian Geographic recounts. When he returned the following year, a crew member named William Hillier died of dysentery, and Flinders named the lake after him, according to EarthDate. The lake is very salty, far saltier than the sea, and that is the key to its colour.
Why Lake Hillier is pink
Very salty water is a harsh place to live, but some microbes, known as halophiles or “salt lovers”, thrive in it. For a long time, the pink of Lake Hillier was credited mainly to one of them, a microscopic alga called Dunaliella salina. In strong sunlight and very salty water, it produces large amounts of beta-carotene, the same orange-red pigment found in carrots, which acts as a kind of sunscreen.
Then, in 2015, researcher Ken McGrath of the eXtreme Microbiome Project collected water and sediment samples from the lake and analysed the DNA of everything living in them. The biggest surprise was that 33% of the millions of DNA sequences from the water matched a single species of bacterium, Salinibacter ruber, a salt-loving microbe that also makes red pigments, Australian Geographic reports. Dunaliella salina was present too, along with other red-pigmented microbes called archaea, as Lake Scientist explains. So the pink seems to come from a whole community of salt-loving microbes, with Salinibacter ruber the most abundant, rather than from one alga alone. Researchers still do not know exactly how much each one contributes to the colour.
Why pink lakes change colour
Pink lakes are not always pink. Their colour depends on a delicate balance of salt, sunlight, temperature and water level. When the water is very salty, the sun is strong and there has been little rain, the microbes produce more pigment and the lake turns a vivid pink. After heavy rain, the water becomes less salty and the colour can fade, and in hot, dry spells, shallow lakes can dry out altogether, leaving only white salt crust. The colour can even change through the day, looking strongest when the sun is high and the sky is clear.
Esperance has its own cautionary tale. The town has a lake actually called Pink Lake, which used to be famously pink and gave Esperance part of its tourist reputation. It has not been reliably pink for years, despite the name, as the Australia’s Golden Outback tourism site warns visitors. The lake sits at the end of a chain of salt lakes, and changes in salinity have upset the balance its pink microbes need. The Shire of Esperance has commissioned scientists to study whether moving salt from nearby Lake Warden could restore the colour, as National Geographic reports. If a lake’s chemistry shifts, the colour can disappear, sometimes for good.
The pink lake that makes food colouring
Western Australia’s most reliable pink lake is Hutt Lagoon, near Port Gregory on the coast between Geraldton and Kalbarri. Its pink comes mainly from Dunaliella salina, and here the alga is not just a tourist attraction but an industry. Hutt Lagoon is home to one of the world’s largest beta-carotene production facilities, run by chemical company BASF, which farms the alga in hundreds of hectares of ponds within the lagoon, as the Royal Australian Chemical Institute’s Chemistry in Australia magazine explains. The harvested beta-carotene ends up in food colouring, supplements and cosmetics, so there is a fair chance you have eaten something coloured by an Australian pink lake.
Other pink lakes around Australia
Australia has more pink lakes than most people realise, and many are far easier to visit than Lake Hillier. In Victoria, Murray-Sunset National Park in the state’s north-west has four pink lakes, Lake Crosbie, Lake Becking, Lake Kenyon and Lake Hardy, according to Australian Geographic. In South Australia, Lake Macdonnell near Penong, on the way to Cactus Beach, can take on a pink hue from certain angles, as Australia So Much to See notes. And Hutt Lagoon is the closest well-known pink lake to Perth, about a five-and-a-half-hour drive north, according to StudyPerth.
Can you swim in Lake Hillier?
It is one of the most common questions people ask about it. The water is extremely salty, but the microbes that colour it are not considered harmful, so in theory you could swim in it, as EarthDate notes; like other very salty lakes, you would float easily. In practice, almost nobody does, because the lake sits within a protected nature reserve on a remote island and is very hard to reach. If you want to experience a pink lake up close, Hutt Lagoon is a far more realistic option, and even there, most people are happy to admire it from the edge.
How to see Australia’s pink lakes
Lake Hillier is the hard one. It sits within a nature reserve on a remote island and is not easy to reach by boat, so for most people the only way to see it is on a scenic flight from Esperance, as WorldAtlas notes. A local cruise operator has also run an occasional full-day boat trip out to the island, Australia’s Golden Outback says, so check with Esperance tourism operators if you would rather go by sea.
Hutt Lagoon is much easier. You can see it from the Port Gregory Road just before the town, and scenic flights also run from Geraldton and Kalbarri, according to Australia Travel Questions. For the strongest colour, go on a clear, sunny day, ideally between about 10am and 2pm, when the sun is high, StudyPerth suggests. The colour depends on how much water is in the lagoon, so it is worth checking recent photos or asking locals before a long drive.
Wherever you go, treat these lakes gently. Stay on marked tracks and viewing areas, do not drive onto lake beds, and check local rules before flying a drone, especially near the commercial ponds at Hutt Lagoon.
Pink by nature
So Lake Hillier is pink because it is so salty that only hardy, pigment-making microbes can live in it, and together they tint the whole lake, with a salt-loving bacterium, not just the famous alga, doing a lot of the work. Every bit of that colour is made by organisms far too small to see without a microscope. If you enjoy the science of colour, my posts on why the sky is blue and whether black and white are colours explain more about why we see the colours we do, and what is the Milky Way? is another good reason to head for Australia’s remote, dark corners.
Sources
- Australian Geographic: How an Australian lake turned bubble-gum pink
- EarthDate: Flamingo-pink lakes
- Lake Scientist: Why Lake Hillier is pink
- National Geographic: Western Australia’s pink lakes
- Chemistry in Australia: Hutt Lagoon, halophile haven
- Australia’s Golden Outback: Why is Lake Hillier on Middle Island pink?
- StudyPerth: Discover WA’s pink lake
- Australia Travel Questions: Hutt Lagoon, best time to visit