EVEN as a kid taking a dip in a friend's swimming pool, Derek Spielman would think about how it would be much better if it was full of turtles. Now his own backyard swimming pool is one of 50 on Sydney's north shore that have been turned into ponds, saving thousands of dollars on power and water bills.
There are no turtles, but Dr Spielman's pool at his home in Gordon is swarming with native fish, such as empire and spotted gudgeons and Pacific blue eye. It's noisy with a chorus of frogs and full of water lilies and other aquatic plants, attracting native birds, dragonflies and bees.
There's not a mosquito in sight (or sound) because the gudgeons eat the mosquito wrigglers. And the mosquito species that live in water deeper than 30 centimetres don't bite humans.
''I wanted to turn our pool into a pond for years,'' said Dr Spielman, adding that it took some time to convince his wife.
After realising that the family of four used the pool only six times in one year, they decided to turn it into a pond.
''It was costing us a lot of time and money, and nobody used it,'' he said.
Most people who don't use their pools think they have only two expensive options: chlorinate or fill them in, said Peter Clarke, the co-ordinator of Ku-ring-gai Council's ''wild things'' program. Few realised if they turned off the power, and stopped chlorinating the water, it would slowly turn into an inexpensive ''giant rainwater tank without a lid'', Mr Clarke said.
Ku-ring-gai's program is special because it actively encourages households to do something good for the environment with their unused pools. Mr Clarke is used to countering arguments from naysayers who presume these pools are dirty breeding grounds for mosquitoes and bacteria.
''When you look at a disused pool, you presume it must be a danger to health. The leaves gather, it is dark on the bottom and you see mosquito wrigglers,'' he said. But random tests for ecoli and other bacteria by the University of Sydney on eight pools converted to ponds found all were within the guidelines for primary water contact.
They're also fine for a quick dip, as Callan Spielman, 23, showed Fairfax Media.
''We've seen pools not looked after for years and years, and the water is always clear,'' Mr Clarke said. These conversions are also reversible.
In some cases, households are using the ponds as biobanks, stocking native fish.
The story Little fish in a big pond save power - and the planet first appeared on The Sydney Morning Herald.