Little Blue Lake is a water-filled sinkhole (“cenote”) in the Australian state of

South Australia South Australia (commonly abbreviated as SA) is a States and territories of Australia, state in the southern central part of Australia. With a total land area of , it is the fourth-largest of Australia's states and territories by area, which in ...

located in the state's south-east in the locality of Mount Schank about south of the municipal seat of

Mount Gambier Mount Gambier is the second most populated city in South Australia, with a population of 25,591 as of the 2021 census. The city is located on the slopes of Mount Gambier (volcano), Mount Gambier, a volcano in the south east of the state, about ...

. It is notable locally as a

swimming hole A swimming hole is a place in a river, stream, stream, creek, spring (hydrosphere), spring, or similar natural body of water, which is large enough and deep enough for a person to human swimming, swim in. Common usage usually refers to freshwate ...

and nationally as a

cave diving Cave-diving is underwater diving in water-filled caves. It may be done as an extreme sport, a way of exploring flooded caves for scientific investigation, or for the underwater search and recovery, search for and recovery of divers or, as in th ...

site. It is managed by the District Council of Grant and has been developed as a recreational and tourism venue.

Naming

The sinkhole's name is attributed to its similar appearance to Mount Gambier’s much larger volcanic Blue Lake and the property of its water to sometimes turn

blue Blue is one of the three primary colours in the RYB color model, RYB colour model (traditional colour theory), as well as in the RGB color model, RGB (additive) colour model. It lies between Violet (color), violet and cyan on the optical spe ...

in colour during summer in a similar manner to the Blue Lake. However in more recent times the sinkhole generally remains

green Green is the color between cyan and yellow on the visible spectrum. It is evoked by light which has a dominant wavelength of roughly 495570 nm. In subtractive color systems, used in painting and color printing, it is created by a com ...

in colour throughout most of the year. This is believed by some to be due to

groundwater pollution Groundwater pollution (also called groundwater contamination) occurs when pollutants are released to the ground and make their way into groundwater. This type of water pollution can also occur naturally due to the presence of a minor and unwant ...

from

agricultural Agriculture encompasses crop and livestock production, aquaculture, and forestry for food and non-food products. Agriculture was a key factor in the rise of sedentary human civilization, whereby farming of domesticated species created f ...

fertilizer A fertilizer or fertiliser is any material of natural or synthetic origin that is applied to soil or to plant tissues to supply plant nutrients. Fertilizers may be distinct from liming materials or other non-nutrient soil amendments. Man ...

s increasing the nutrient levels. The lake is also known as Baby Blue and is referenced in caving literature by its Cave Exploration Group of South Australia (CEGSA) Inc. identification number 5L9.

Description

The lake is located approximately south of the City of Mount Gambier, on the north side of Mount Salt Road (near Mount Schank) about west of the Riddoch Highway, which is the main road between Mount Gambier and the coastal fishing township of Port MacDonnell. The sinkhole is located on

crown land Crown land, also known as royal domain, is a territorial area belonging to the monarch, who personifies the Crown. It is the equivalent of an entailed estate and passes with the monarchy, being inseparable from it. Today, in Commonwealth realm ...

in section 963 in the cadastral unit of the Hundred of MacDonnell. The sinkhole’s lake has a diameter of about , with surrounding vertical/undercut cliffs about high. Access to the water’s edge is via an artificial

cutting Cutting is the separation or opening of a physical object, into two or more portions, through the application of an acutely directed force. Implements commonly used for wikt:cut, cutting are the knife and saw, or in medicine and science the sca ...

on the southern side of the sinkhole and a metal stairway that leads to a small floating pontoon. The silty bottom of the lake is very flat with an average depth of about ; its shallowest point is around at the top of a rubble pile directly beneath the cut access ramp/pontoon, and a dark, silt-prone region extends around the southern/western sides of the sinkhole’s bottom to a maximum recorded depth of just over 42 metres (depending on regional water-table fluctuations). The underwater visibility is normally poor, but can at times improve at depth and seasonal/longer-term changes in the regional water table can result in high/low variations of around . A notable feature of the lake is the accumulation of rubbish dumped in the lake over the years including a 1966 Morris 1100, an old petrol

bowser , also known as King Bowser or King Koopa, is a Character (arts), fictional character and the Antagonist, main antagonist of Nintendo's ''Mario (franchise), Mario'' franchise."The Top 100 Videogame Villains". IGN. Retrieved October 8, 2010. ...

traffic sign Traffic signs or road signs are signs erected at the side of or above roads to give instructions or provide information to road users. The earliest signs were simple wooden or stone milestones. Later, signs with directional arms were introduc ...

s and ’witches hats’.

Geological origins

The Little Blue Lake is one of a number of similar landforms occurring in the area to the south of the dormant volcano in Mount Gambier including the area around the dormant volcano at Mount Schank. These cenotes are similar in form as they all have collapse dolines with circular plans, cliffs, lakes filled to the water table, large rubble cones on their floors and clustered together in several groups along in the flat coastal plain composed of a

Miocene The Miocene ( ) is the first epoch (geology), geological epoch of the Neogene Period and extends from about (Ma). The Miocene was named by Scottish geologist Charles Lyell; the name comes from the Greek words (', "less") and (', "new") and mea ...

limestone known as Gambier Limestone. These cenotes differ from other

karst Karst () is a topography formed from the dissolution of soluble carbonate rocks such as limestone and Dolomite (rock), dolomite. It is characterized by features like poljes above and drainage systems with sinkholes and caves underground. Ther ...

landforms in the south east of South Australia by their relative depth (i.e. as deep as in one cenote), the absence of any underwater

phreatic ''Phreatic'' is a term used in hydrology to refer to aquifers, in speleology to refer to cave passages, and in volcanology to refer to a type of volcanic eruption. Hydrology The term phreatic (the word originates from the Greek , meaning "well" ...

passages and a different water chemistry. It is theorised that these cenotes were formed by the collapse of large underground water-filled chambers following the lowering of sea levels at the most recent Glacial Maximum about 20,000 years ago. The chambers themselves are likely to have been formed by groundwater acidified by gaseous

Carbon Dioxide Carbon dioxide is a chemical compound with the chemical formula . It is made up of molecules that each have one carbon atom covalent bond, covalently double bonded to two oxygen atoms. It is found in a gas state at room temperature and at norma ...

(CO₂) rising up through fractures from the magma chambers during the volcanic eruptions occurring during the

Pleistocene The Pleistocene ( ; referred to colloquially as the ''ice age, Ice Age'') is the geological epoch (geology), epoch that lasted from to 11,700 years ago, spanning the Earth's most recent period of repeated glaciations. Before a change was fin ...

and the

Holocene The Holocene () is the current geologic time scale, geological epoch, beginning approximately 11,700 years ago. It follows the Last Glacial Period, which concluded with the Holocene glacial retreat. The Holocene and the preceding Pleistocene to ...

rather than by the usual acidification process involving the absorption of atmospheric CO₂ by water prior to entering the water table. The cenotes then filled with freshwater as the sea level started to rise at about 8,000 years ago. The presence of

stromatolites Stromatolites ( ) or stromatoliths () are layered sedimentary formations ( microbialite) that are created mainly by photosynthetic microorganisms such as cyanobacteria, sulfate-reducing bacteria, and Pseudomonadota (formerly proteobacteria) ...

in at least eight cenotes including the Little Blue Lake is suggested as being an indicator of the recent formation of these landforms.

Exploration

Exploration of the lake's underwater environment commenced in the 1950s. The lake’s submerged extent was surveyed by Lewis and Stace in 1980 and by the Cave Divers Association of Australia (CDAA) during the 1990s.

Present day

The lake is a popular venue for swimming and cave diving. The land which includes the sinkhole was dedicated as a reserve "for the purposes of a Public Pleasure Resort" under the ''Crown Lands Act 1929'' on 19 March 1986 and placed under "the Care, Control and Management" of the former District Council of Port MacDonnell. The District Council of Grant installed stairs and a floating pontoon in 2002 to improve the lake’s amenity for both residents and visitors after a review of public safety. A parking area also exists on the lake's east side. Diving in the sinkhole is only permitted for cave divers who hold at least the CDAA Deep Cavern grade rating.

References

External links

Little Blue Lake Cliff Jumping
{{DEFAULTSORT:Little Blue Lake Sinkholes of Australia Limestone Coast Underwater diving sites in Australia Lakes of South Australia Swimming venues in South Australia