We had some ice on our pond for the first time last week. Will this affect our goldfish here?

As the water temperature falls, so the fish will move to the deeper part of the pond, where they should be free from any risk of becoming caught in the ice, remaining largely dormant. The pond must be at least 0.9m (3ft) in depth to ensure their safety. A solid covering of ice over the entire surface of the pond will mean that harmful gas, resulting from the decay of aquatic vegetation, cannot pass out into the atmosphere.

It will then accumulate in the water, representing a threat to the fish at a time when they are at their most vulnerable, unless the ice is broken. Ideally therefore, you should always clean out the pond in the autumn, removing as much old vegetation such as water-lily leaves and flowers as possible, to reduce this risk.

When ice has formed on the water, avoid using a hammer to smash a hole through it. This is not just because the shock waves may be upsetting to the fish, but you could also damage the pond itself, particularly if it is a moulded design. Instead, boil a saucepan of water, and gently use this to thaw a hole in the ice. Take care not to spill any of this water on yourself or into the pond though, simply keeping the hot base of the saucepan in contact with the ice to melt it.
 
Air hole in pondIt will be better to reduce the risk of the water freezing in the first place. If you have access to a safe external electrical supply, then it is possible to obtain a pond heater for this purpose.

Fountain in goldfish pondThis type of heater will not stop the entire surface from freezing over, but it will ensure that there is an area around the heater itself which remains free from ice.

Alternatively, keeping a fountain running, if you have one in your pond, can also help to prevent ice forming here where the water is moving. If the weather is forecast to be very cold, this is not recommended though, as the fountain its may freeze.

A cheaper but less reliable option is simply to place a clean plastic football on the surface of the pond when the weather forecast suggests that the temperature will fall below freezing. This is a particularly useful method on windy nights, because the movement of the ball should then serve to keep the surface free from ice.  Even if the water does freeze however, it should be possible to prise out the ball without too much difficulty, leaving a hole beneath in the ice. 

* For further information about the relative hardiness of different varieties of goldfish, and feeding them through the autumn and winter, click here.