Lake Hillier is a saline lake on the edge of Middle Island. It is particularly notable for its pink colour. A long and thin shore divides the Southern Ocean from the lake. The vibrant colour is permanent, and does not alter when the water is taken in a container. The pink colour is considered to be due to the presence of the organism "Dunaliella salina". At one point in its history the lake was used to collect salt.

The only living organisms in Lake Hillier are microorganisms which causes the salt content in the lake to create a red dye which helps produce the colour, as well as red halophilic bacteria present in the salt crusts. Despite the unusual hue, the lake exhibits no known adverse effects upon humans. From above, the lake appears a solid bubble gum pink, but from the shoreline it appears more of a clear pink hue. The shoreline is also covered in salt crust deposits.

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