are a series of three limestone sinkholes
on Eight Mile Creek south of Mount Gambier
and east of Port Macdonnell
, South Australia
. The ponds are popular with scuba divers
, with underwater visibility of up to 80 metres (264 feet) and a large fish population including the endangered golden pygmy perch
The original inhabitants of the land were Aborigines
of the "Boandik" tribe, part of a larger "Bunganditj" clan. The first European identified with the area was Thomas Ewens, whose dog chased a kangaroo into one of the ponds. The land surrounding the ponds was gradually cleared for agriculture and dairy farming
and a drainage system built to draw water from the ponds for land sold for soldier settlement
programs post-World War Two
In 1978 a trout farm was established utilising the waters flowing through Ewens Ponds. Although the ponds themselves are now part of a conservation park, the farm continues to operate. Water for the farm is drawn from the second pond, and wastewater discharged back into Eight Mile Creek downstream from the pond system.
Each pond is a basin-shaped limestone cenote
approximately ten metres (30 feet) deep and connected to the others by shallow watercourses. The beds are covered with a fine silt layer and the floor of the third pond also contains a natural shallow cave. The ponds are located in a narrow band of native bush land, surrounded by cleared terrain. The landscape is characteristic of karst topography
, shaped by the gradual dissolution of soluble limestone to form hollows and small caves.
The ponds' excellent water quality allows underwater visibility of up to 80 metres (264 feet), and sufficient natural light for plant growth on the pond beds to reach up to six metres in height. The ponds are occasionally affected by blue-green algae, though testing has found no evidence of health risks. In 2007 the South Australian Environmental Protection Agency suggested the algal blooms may be a result of continued concentrations of soluble nitrogen in both the ponds and the adjoining Eight Mile Creek, arising from infiltration of the groundwater by fertilisers, animal waste or wastewater.
The ponds are one of only three recorded locations for the golden pygmy perch (Nannoperca variegata
). Other fish life includes schools of short-finned eel
, river blackfish
, pouched lampreys
and common galaxias
. The ponds are also home to populations of flatworms
, freshwater crayfish
, and the larva of the carnivorous caddis fly
The pond beds are formally owned by the South Australian Department of Water, Land and Biodiversity Conservation and managed as a conservation park by the Department of Environment and Heritage. Plant and animal species in the ponds are protected and may not be removed.
High visibility and a substantial fish population have made the Ponds popular with scuba divers.. Of particular interest in these clear waters is the actual observation of photosynthesis. Water plants can be seen releasing thin trails of bubbles as they convert sunlight into oxygen. However divers are prohibited from entering caves or crevices on the pond beds and strongly discouraged from disturbing the silt layer as the resulting turbidity may harm plant life. Of particular concern is the practice of divers returning through the channel linking the three ponds, thereby disturbing the water plants lining the channel. Water temperatures range from 10 to 15 degrees.