arrow_back In Mount Gambier South Australia · Natural Wonder

Blue Lake

The Volcanic Crater Lake That Changes Colour

location_on Mount Gambier

schedule 2 min read / Updated Apr 2026

A crater lake in an extinct volcano at Mount Gambier that turns a vivid cobalt blue from November to March each year, then fades back to steel grey for the southern winter. The colour change has been the subject of scientific curiosity since the 19th century.

Blue Lake sits in the crater of Mount Gambier, an extinct volcano that last erupted around 4,300 years ago, making it one of the youngest volcanoes on mainland Australia. The lake is about 1.2 kilometres long, 75 metres deep at its deepest point, and is the main drinking water supply for the city of Mount Gambier.

The lake is famous for its dramatic seasonal colour change. From November to March each year, the water turns a vivid cobalt blue, almost unnaturally so, and then fades back to a dull steel grey for the rest of the year. The exact mechanism is still debated by scientists, but the most accepted explanation involves calcium carbonate crystals that form in the warmer summer water and scatter blue light in the same way the sky does. The shift happens rapidly, usually over a few weeks in November, and is most intense in January.

A sealed road runs the full 3.6 kilometre perimeter of the crater and there are several lookouts at different elevations. The Kennedy Point lookout on the north side gives the most photographed view, with the water directly below and the town of Mount Gambier on the horizon. The Aquifer Tours guided descent takes small groups down a glass-walled elevator to the pump station at the water line, offering the only public access to the water itself.