Little Blue Lake is the most accessible sinkhole in the Mount Schank field and one of Mount Gambier's best-known swimming holes. It is a near-circular collapse sinkhole about 50 m across, ringed by vertical cliffs roughly 8 m high, sitting right beside Mount Salt Road. Underwater it is essentially a bowl: steep walls fall to a very flat silt floor with an average depth of about 36 m and a maximum of a little over 42 m, while the shallowest bottom, near the access ramp, is around 25 m.

It is not a showpiece like Kilsby's. The CDAA's own listing is blunt – a local swimming hole with rubbish on the bottom, dirty water and poor visibility that can be clear below 20 m – and divers who come expecting Piccaninnie clarity are disappointed. What it offers instead is easy access, genuine depth and a realistic low-visibility environment that is useful for Basic Cave training, depth practice and equipment checks. Descending through a green surface layer into darker, clearer water below the thermocline is a common Little Blue experience, and the flat floor makes it easy to hold a stable depth. Rubbish thrown in over the decades lies on the bottom.

Exploration began in the 1950s, it was surveyed in 1980 and through the 1990s, declared a public pleasure resort in 1986 and handed to council management; the District Council of Grant built the cutting, staircase and pontoon in 2002. Swimmers share the site, so dive early. It suits CDAA Basic Cave divers who want a simple, deep freshwater dive with no booking hassle, and trainees on CDAA courses.

From Mount Gambier drive south on the Riddoch Highway towards Mount Schank/Port MacDonnell (about 20 km), turn onto Mount Salt Road; the lake is right beside the road with a parking area on its east side. From the car it is a short walk to the top of the cutting, then down the metal staircase (installed 2002) to the floating pontoon – an easy gear carry by Mount Gambier standards. The CDAA provides a change table.

No booking system is listed on the CDAA page, but diving is restricted to CDAA members holding at least Basic Cave (former Deep Cavern).

Sheltered by 8 m cliffs; weather rarely stops a dive, but summer brings algae and poor surface visibility, and hot weekends bring swimmers and jumpers onto the pontoon – dive early or midweek. Visibility improves seasonally at depth, and water below 20 m can be clear when the surface is murky. Heavy rain washes road run-off in.

Total Fire Ban days do not close this council site but check signage.

Descend from the pontoon down the slope below the access ramp (shallowest part about 25 m) through the murky upper layer, level off above the flat silt floor at 30-36 m within Basic Cave limits, circle along the wall, and ascend slowly up the wall to a safety stop under the pontoon.

CDAA grade: Basic Cave (5L9), owner District Council of Grant/Port MacDonnell council. No overhead. Primary light essential below the murky layer; consider a reel/line on the wall in low vis.

Air suitable within 40 m limits; nitrox for shallower long dives.

No commercial scuba tours; dived independently by CDAA Basic Cave members and on CDAA Basic Cave courses (Diving Adelaide, Deep Blue Ventures, CDAA instructors). Swimmers use it freely in summer.