A microbial masterpiece
On Middle Island, off the coast of Western Australia, lies Lake Hillier, a body of water roughly 600 meters long and 250 meters wide with a bright, bubblegum-pink color. From the air, the lake appears as a solid pink oval, separated from the deep blue of the Southern Ocean by a thin strip of sand and dense paperbark and eucalyptus woodland. The English navigator Matthew Flinders was the first European to document the lake on January 15, 1802, after climbing the island's highest peak. He recorded in his journal "a small lake of a rose colour" with water so saturated with salt that crystals formed near the shores.
The lake's permanent pink hue is the result of a specialized community of microorganisms thriving in its hypersaline water. The salinity of Lake Hillier is comparable to that of the Dead Sea, often ten times saltier than the ocean. This extreme environment is inhospitable to most life, but it is home to certain extremophiles. One of the main organisms responsible for the color is the microalga Dunaliella salina. To protect itself from the intense solar radiation in the shallow lake, D. salina produces large amounts of protective carotenoid pigments, particularly beta-carotene, the same pigment that gives carrots their orange color.
The full color palette
While Dunaliella salina was long thought to be the sole cause, recent metagenomic analysis reveals a more complex picture. The lake's color is a "cocktail" created by several microbes. Red halophilic bacteria, a type of archaea, are also major contributors. These organisms, such as Salinibacter ruber and various species of Halobacterium, live in the salt crusts and produce their own reddish pigment called bacterioruberin.
The final, pink shade of the lake comes from the pigments from this diverse community of archaea, bacteria, and algae. The intensity of the color can shift slightly with changes in temperature and sunlight, which influence the life cycles and pigment production of the microbes. Unlike some other pink lakes that can change color seasonally, Lake Hillier's pink hue is stable and remains even when the water is collected in a container. Recent heavy rainfall has occasionally diluted the lake and temporarily faded its color, but the pink is expected to return as salinity levels reconcentrate.