Blue Lake / Warwar

Blue Lake / Warwar (The Blue Lake) is a large, monomictic, crater lake located in a dormant volcanic maar associated with the Mount Gambier maar complex. The lake is situated near in the Limestone Coast region of South Australia, and is one of four volcanic crater lakes originally on Mount Gambier maar. Of the four lakes, only two remain, the other one being Valley Lake / Ketla Malpi; the other two, Leg of Mutton Lake / Yatton Loo and Brownes Lake / Kroweratwari, dried up as the water table dropped.

History
Conflicting dates have been estimated for the last eruption of the volcano: of 4,300 years ago, of 28,000 years ago, and a little before 6,000 years ago. If the youngest date is correct, this could be the most recent volcanic eruption on the Australian mainland.

The Boandik (or Bungandidj) people occupied the area before the colonisation of South Australia.

Description
Blue Lake / Warwar is one of four lakes in the Dormant volcano complex. Sites of cultural significance to the Boandik people were assigned dual names by the City of Mount Gambier in February 2022, and the renaming included the four lakes in the Bungandidj language. These are as follows:
 * Blue Lake / Warwar, meaning "crow country"
 * Leg of Mutton Lake / Yatton Loo
 * Brownes Lake / Kroweratwari, meaning "emus, [or] their tracks"
 * Valley Lake / Ketla Malpi, meaning "sacred talking tree"

Blue Lake is thought to be of an average depth of 72 m, but in places reaches 75 m deep (but some unconfirmed values mention a 204 m maximum depth due to a natural cave section). The crater rim measures 1200 by, but the lake itself measures 1087 by. The surface of the lake is 17 m below the level of the main street of the nearby town. The Blue Lake supplies the town with drinking water.

Browne's Lake / Kroweratwari (sometimes spelt Browns Lake) dried up in the 1980s, and is now a picnic spot.

There is a 3.6 km road and walking track around the circumference of Blue Lake / Warwar, with an underpass between it and Leg of Mutton Lake / Yatton Loo.

Annual colour change
Each November, the lake turns to a deep turquoise colour, gradually returning to a duller blue colour in late February to March. The exact cause of this phenomenon is still a matter of conjecture, but likely it involves the warming of the surface layers of the lake during the summer to around 20 C, causing calcium carbonate to precipitate out of the solution and enabling microcrystallites of calcium carbonate to form. This results in scatter of the blue wavelengths of sunlight. During winter, the lake becomes well mixed, and recent research indicates that during this phase of the colour cycle, the lake is somewhat murkier due to the redistribution of tannins and calcium carbonate particles throughout the lake. Solar elevation has also been found to influence the perceived colour of the lake. The movement of planktonic life forms within the lake during the seasons and during the day may additionally play a part in the colour change.

Studies
Bathymetric surveys located the deepest point in the lake at 77 m in 1967. Major diving exploration of the lake first occurred in 1985. Cave diver Peter Horne conducted temperature and visibility studies and made discoveries of a freshwater sponge species and other invertebrates. This exploration also discovered the Stromatolite Field, a collection of hollow rock formations that are found along the north-eastern perimeter down to a depth of 40 m. In 2008, permission was granted by SA Water for another diving exploration of the central and deepest parts of the lake. On this dive, core samples from the calcite-silt covered lake bed were collected where water temperature drops to 14 C.

Gordon's leap
In July 1865, Adam Lindsay Gordon performed the daring riding feat known as Gordon's Leap on the edge of the Blue Lake. A commemorative obelisk erected there has an inscription which reads: "This obelisk was erected as a memorial to the famous Australian poet. From near this spot in July, 1865, Gordon made his famed leap on horseback over an old post and rail guard fence onto a narrow ledge overlooking the Blue Lake and jumped back again onto the roadway. The foundation stone of the Gordon Memorial Obelisk was laid on 8th July 1887"