Water temperature plays an important role in controlling beneficial organisms. If you have fish in your ponds, then they may die during the winter months if the water temperature drops too low. Lower temperature also hamper the basic physiological functions of fish. If you live in the southern or interior parts of Australia, the surface of your pond water may freeze overnight during winter, which will reduce the gaseous exchange. Heating your pond water is highly advised if you live in the colder regions of Australia.
As a rough guide you will require at least 1 watt of heating for every 1 litre of pond water. Aqua Gardening offers one of the best water heaters to increase the water temperature of your pond. Check out the Aqua One Glass Water Heater, which is able to control the temperature between 20 to 34 degrees Celsius via an adjustable thermostat.