From April to November - the lake is a colder steelgreycolour.
A change occurs around mid November.
From December to March - the lake is a vibrantcobaltblue!

You can see this from the photos here. The lake is impressive during winter, but absolutely spectacular in summer.
Notice the colour change, and also the difference in colour between the Blue Lake and the nearby Valley Lake.

Blue Lake FebruaryBlue Lake - February

Color of the Blue Lake over the course of a typical year

Blue Lake MayBlue Lake - June Blue Lake OctoberBlue Lake - October Blue Lake DecemberBlue Lake - December Blue Lake FebruaryBlue Lake - February Valley Lake (more green than blue)Valley Lake (more green than blue) Valley Lake (more green than blue)Valley Lake (more green than blue)
Why Is The Blue Lake Blue?

The exact cause is still not certain, however it is generally considered likely that it revolves around the warming of the surface layers of the lake during the summer months to around 20 degrees Celsius (70 F).  Some say this causes calcium carbonate to precipitate enabling micro-crystallites of calcium carbonate to form, resulting in the blue wavelengths of light to be scattered, giving the lake its brilliant blue appearance.

During winter the lake becomes well mixed, and recent research indicates that during this phase of the colour cycle the lake is somewhat murkier due to the redistribution of tannins and calcium carbonate particles throughout the lake.

Solar elevation and weather have also been found to influence the perceived colour of the lake, but only by 16%, so the lakes properties themselves are probably the main influence of the colour.

The visability in the lake in winter is around 9 meters, but in summer it's about 17 meters.

Why Is The Blue Lake Blue?

The lake changes colour dramatically over a few days in November each year.  Then after summer it gradually fades until the grey winter appearance resumes.

The lake was formed by volcanic activity and is thought to be one of the youngest volcanoes in Australia.

The water quality of the lake is very good and is used as Mount Gambier's water supply.  The lake is flat bottomed with an average depth of 70 meters, and a volume of 36,000 million litres.  It has a circumference of 5 kilometers and is a favorite walking track for all who wish to keep fit and enjoy the beautiful scenery.

Blue Lake view 1 Blue Lake lookout Blue Lake and pumphouse