Meet the site
The Blue Lake is Mount Gambier's emblem and the source of the city's drinking water, and it is included here because divers constantly ask about it. It is a volcanic maar crater lake: the crater rim measures about 1,200 x 824 m and the lake about 1,087 x 657 m, with a basically flat floor averaging around 72 m deep and a deepest point of 77 m recorded in 1967. The water is high-quality groundwater from the limestone aquifer.
Its fame comes from colour. Each November the lake turns a vivid turquoise-cobalt, gradually returning to a duller blue or steel grey from late February to March. The likely mechanism is calcium carbonate precipitating as microcrystallites in warmer months, scattering blue light.
Recreational diving and swimming are not permitted because the lake is a protected public water supply. Diving has happened only as authorised research. In 1985 cave diver Peter Horne led a major exploration that found freshwater sponges and the lake's Stromatolite Field, and he coordinated four more studies up to 1991; another exploration was authorised in 2008 under Dr Richard Harris. The lake is also known for syncarid crustaceans shared only with Fossil Cave.
For visiting divers, the Blue Lake is a surface attraction: walk the rim, take the Aquifer Tour down the old pump shaft, and then go and dive Kilsby's, Ewens or – with the right CDAA grade – the region's caves. It is not a dive site and should not be treated as one. The lake is also a major tourist site, so treat it as a rest-day stop.
Research this site before booking Stored site notes may be historical. These questions highlight gaps without turning old instructions into a current dive plan.
Blue Lake (Mount Gambier) is recorded as Freshwater Lake/River in Mount Gambier Sinkholes & Caves. The listed access is shore. Confirm the actual meeting point, route and permission to visit; a map pin does not establish any of these.
Historical access notes exist for this record, but have not been independently verified for current use. Request current directions from the operator or site manager rather than following an old entry description.
Questions, answered
Is Blue Lake (Mount Gambier) suitable for my certification?
The record lists Technical (decompression). That does not establish suitability for every route or day. Share your training, recent experience and equipment needs with the operator and ask about the specific proposed dive.
Can I book Blue Lake (Mount Gambier) through YouDive?
YouDive is an independent research directory. Contact an operator directly to confirm whether it currently runs the trip, the inclusions and the booking terms.
What you might see
Stromatolites, freshwater sponges, syncarid crustaceans (documented by research dives)
Location
Mount Gambier's 72-77 m-deep volcanic crater lake (about 1,087 x 657 m) on the city's southern edge; the city's drinking-water supply. NO recreational diving or swimming.
Facilities nearby
Lookouts, parking, rim walking track, Aquifer Tours; cafes and all services in Mount Gambier.
Before you make plans
Conditions, access and operator schedules can change. This is a location guide, not a dive plan. Ask a local operator about current conditions and suitability for your training and experience.
Sources & further reading
en.wikipedia.orgen.wikipedia.orgRecord updated 26 Sept 2026. Source claims are being reviewed.