Lake Hillier or lake Hillier is a pink lake located on Middle Island, which is part of the Recherche Archipelago group, on the southern coast of the state of Western Australia.

The discoverer of Lake Hillier was Mathew Flinders, an English navigator. In January 1802, Flinders and the crew of the HMS Investigator docked on Middle Island. In his notes, Flinders wrote he was surprised to see a "little rose-colored lake". He named the lake Hillier in memory of William Hillier, a crew member who recently died of dysentery while anchored on the island.

Scientists are still not sure why this lake is pink. Most suspect this is caused by the microalgae Dunaliella salina. Dunaliella produces carotenoids, the pigments found in carrots. Another theory also suggests that the pink color could be due to the presence of halophilic bacteria in the salt crust. The reaction between the salt and the sodium bicarbonate found in water produces a pink color.

Even though it is pink in color, scientists have confirmed that the water in the 600-meter-wide and 250-meter-wide lake is harmless to human skin. However, you cannot swim or drink water in this lake because it is located on a remote island. For tourists who want to enjoy the beauty of this lake, they can see it from the waters by renting a boat or from the air by renting a small plane.

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