The common question asked by visitors and Mount Gambier residents for eons is: how does Mount Gambier’s Blue Lake turn such a brilliant hue?
Visit in winter and you’ll wonder what the hype is about, but visit in summer and it will be made clear. Almost overnight the lake transforms from a wintery steel grey to embrace summer wearing a magnificent coat of cobalt blue.
Theories abound at this mysterious phenomenon. Is the lake bottomless? Is the colour reflecting the sun? Does a certain algae contribute? Is it a chemical reaction with limestone? Or, is it a story from the Dreamtime where an ancient bunyip rises to the surface to greet the summer sun?
Are you curious? Then let’s find out!
Mount Gambier in south eastern South Australia, halfway between Adelaide and Melbourne, is 17 kilometres from the S.A. - Victoria border. This coastal limestone region provides a sponge below the surface maintaining a water table feeding the lush landscape.
Part of a volcanic terrain of craters and caves within the Kanawinka Geotrail, this volcanic area has over 60 accessible sites offering waterfalls, lakes, caves and the opportunity to climb into one of the regions youngest volcanoes.
The Blue Lake is one of 4 of Mount Gambier’s craters located just 10 minutes from the town centre. It’s last eruption is considered by geologists to be quite recent - 4,000 to 6,000 years ago!
Is it bottomless?
We can dispel the “bottomless” theory as divers in the 1980’s measured the depth at an average of 70 metres, reaching 77 metres at its deepest point.
Is it reflecting colour from the sun? Does a certain algae contribute? Is it a chemical reaction with limestone?
According to Andrew Telfer and Kylie Hyde of Australian Water Environments P/L, light, algae, limestone and inflowing groundwater chemistry all contribute.
As sunlight enters the lake a small proportion comes back out. In summer, the range of light coming out of the lake is dominated by blue while in winter it’s green.
The lake water flows in through limestone rocks and as the lake warms in summer calcite precipitation occurs removing humic substances (dead algae and land vegetation) which are yellow in colour lessening the green shade.
Exploring the Lakes.
The Blue Lake is 500 metres across and a 3.6km path follows the circumference. Viewing platforms placed at intervals allow for wonderful photographic opportunities. Take a leisurely walk, jog or drive around the perimeter of the lake to appreciate its beauty.
To get closer to the lake’s surface take the Aquifer Tour. A glass panelled lift descends the original dolomite wall shaft and through a tunnel to the lake. The 45 minute tour explains the hydrology of Mount Gambier’s water supply, the aquifer system, the area’s geology, history and Aboriginal legends.
The many walking trails around the lake area provide an excellent outdoor workout. Leg of Mutton and Valley Lake have walking trails with viewing points taking in the city, lakes, park and surrounds. Alternatively, BBQ areas between Valley Lake and Browne’s Lake provide a perfect reason to relax and spend the day.
Although scientists have a water tight explanation for the colour changing phenomenon of the Blue Lake, I still prefer to think there is an ancient bunyip coming up from the depths every summer to warm its back and shine its blue armor through the surface.
Dreamtime legends: they’re things we love….
Shona’s award winning travel blog shares tips and tricks on where to eat, drink, explore & shop in any given destination. At home ordering street food or perusing a fine dining menu, she seeks out venues with a conscience who promote local produce and sustainability. Find her in markets, museums, art galleries and on walking tours as well as wineries, breweries, distilleries and restaurants. Wherever she is, she’s always looking for something a little different to share with her readers. Follow her travels at www.paraphernalia.co or subscribe to her Shenanigans Report http://paraphernalia.co/subscribe-form/ so as not to miss a post. email@example.com.