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 six feet 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, according to district ranger for the Department for Environment and Water Ross Anderson.