Blue Lake is a large lake located in an extinct volcanic caldera in Mount Gambier. It is known as Waawor in the local Aboriginal language. During summer and the surrounding months, the lake takes on a vibrant blue colour, returning to a colder steely-grey colour for winter. The exact cause of this phenomenon is still a matter of conjecture but it is generally considered likely that it revolves around the warming of the surface layers of the lake during the summer months to around 25 degrees celsius, causing calcium carbonate to precipitate out of solution and enabling micro-crystallites of calcium carbonate to form. This results in a scatter of the blue wavelength of sunlight. The movement of planktonic life-forms within the lake during the seasons and during the day may also play a part in the visibility changes.