In the spring-fed waters of three basin-shaped ponds in south-east South Australia, the water is so clear that plants can grow even 2 metres down, something not seen anywhere else in the world, an expert says.

Located about 25 kilometres south of Mount Gambier, Ewens Ponds is situated in a spring-fed limestone sinkhole.

Even on a scorching hot day, the ponds’ freshwater remains at a constant 16 degrees Celsius, according to district ranger for the Department for Environment and Water Ross Anderson.

Ewens Ponds is situated in a spring-fed limestone sinkhole.(Supplied: Michel Roggo)

“Because of the flow rate down here with the ponds emptying out and replacing with water every 16 hours, it never really gets a chance to heat up,” Mr Anderson said.

“It’s not as if it taps turns every 16 hours, but it takes 16 hours for the ponds to completely change their water from the spring flow.”

Environment provides the goods for underwater plants

Mr Anderson said the clear water allowed light to travel to the bottom of the ponds and the growth of plants like water ribbons and rush-like plants.

“A lot of these species don’t exist at that sort of depth anywhere else. Because the water is so clear here, they can grow to a lot deeper than they would anywhere else,” he said.

“In other places, these plants are just living on the surface in very shallow water or even areas that they don’t have water.”

The ecosystem supports a range of unique species, including the Ewens pygmy perch, which is exclusive to the area.

Mr Anderson said the pure filtered water was also quite old.

Some plants found in Ewens Ponds can’t be grown while submerged in water anywhere else in the world.(Supplied: Michel Roggo)

“It depends a little bit on where the springs are coming from within the ponds themselves, but it’s in the order of 30 or 40 years old that this water has been filtered through the limestone before it ends up here,” he said.

Changed landscape

Mr Anderson said many of the areas surrounding the Ewens Ponds were once wetlands only decades ago.

Uncle Ken Jones, a traditional elder of Boandik Country, has been invited to help with the re-wetting of certain areas, similar to a program he was involved with in the early 2000s.

“It worked so well in those couple of years of trial, we’re looking at doing it again in other areas,” he said.

“Simply lifting the water table a couple of hundred millimetres can mean we can re-wet our amazing wetlands.”

The water in Ewens Ponds is always 16 degrees as new water flows in every 16 hours.(Supplied: Michel Roggo)

Uncle Ken said the wetlands were important in preserving animals that swam in and out of the nearby ocean.

“The geese and the prickly back crayfish … all these animals are almost lost, so what a great opportunity to be involved in getting some help with volunteers and like-minded land managers,” he said.

“We can turn it around a bit and save some valuable gems.”

Ewens Ponds is open to the public for scuba diving and snorkelling. A wetsuit is recommended.

A permit is required, with bookings available through the state’s National Parks and Wildlife website.

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