Blue Lake (South Australia)

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The Blue Lake in early March with the original pumping station in the foreground.

The Blue Lake (37°50′S 140°46′E) in Mount Gambier is a large lake located in an extinct volcanic caldera. It is known as Waawor in the local Aboriginal language.

During summer (December to February) and the surrounding months, it appears to be a vibrant blue colour, returning to a more normal colour for winter.

An explanation for this phenomenon is that carbon dioxide degasses from the magma and rises to surface, reacting with the limestone underneath the lake. This reaction dramatically increases the concentration of calcium dissolved in the water. The change in temperature of the calcium-rich lake causes the calcium to become supersaturated and precipitate out of the solution. Micro-crystallites of calcium carbonate scatter the blue wavelength of sunlight.

The Blue Lake supplies the town with drinking water, providing approximately 3,600 ML per year from its 36,000 ML store. Its average depth is 70 m.

The Blue Lake in early March.

The Blue Lake in early March.

The Blue Lake in early March.

Approximately 4 metres above the lake's surface.