frozen fish ponds
Does your koi/fish pond look like this in winter? Well read on...

What If The Koi Pond Freezes In Winter?
What To Do With Frozen Fish Ponds.

Frozen koi ponds or gold fish ponds are generally referred to when the surface of the fish pond is frozen. This is the type of frozen fish pond we will discuss on this page… better described as a fish pond frozen over or a garden fish pond with a layer of ice.

You might have searched for:

• Frozen Koi Ponds & Fish Ponds.
• Ponds Freeze in Winter.
• Pond Care in Freezing Winter Weather

How Pond Water Freezes

The following is the process whereby water in a frozen fish pond actually freezes:
The air temperature drops below pond’s water freezing point (0C/32F). A thin film of ice forms over the surface of the koi fish pond. The term frozen fish ponds implies a solid lump of frozen fish pond.
NOTE: Only in the very worst Siberian type winters and shallow ponds does a pond freeze solid.

Frozen koi or gold fish ponds are generally referred to when the surface of the fish pond is frozen. These are the type of frozen fish ponds we will discuss on this page… better described as a fish pond frozen over or a garden fish pond with a layer of ice.

How Ice Forms on a Pond

As long as the air temperature is below freezing point of pond water (zero degrees Centigrade/32 degrees Fahrenheit) the layer of ice on the fish pond surface will gradually get thicker. As the ice layer gets thicker on the fishpond it becomes a kind of heat insulator and the rate of temperature drop in the water below the fish pond ice surface falls. And this is what is really clever and allows us all not just koi or other pond fish to survive.

Water Has Its Maximum Density at 4° C/39.2° F.

Water has an important physical property and is unique in this behavior. It is this property that allows aquatic life including pond fish to survive when severe freezing in winter takes place. Let me explain what happens with frozen fish ponds as water freezes, trapping the fish below a solid surface preventing any air or oxygen transfer from the air to the water.

The density of liquids increase as temperature of the liquid drops. So you might expect the cold surface pond water of zero degrees C/32.0 °F would drop to the bottom of the fish pond. If this was the case fish pond water would then freeze from the bottom up.

Water has its maximum density not at zero degrees but at 4° C/39.2° F. This means water below 4 degrees/39.2° F will rise to the surface and insulate the lower levels of fish pond water. Ice formation on the koi pond surface also insulates the fishpond water to the extent that it is extremely rare that a fish pond of any kind and any lake for that matter will freeze solid.

How do Koi & Other Fish Survive

If you measured the bottom layer of pond water in a frozen fish pond you would get a measurement of 4 degrees/39.2° F. At this temperature fish are very sluggish and therefore consume little oxygen in frozen fish ponds. This is how koi or other pond fish survive a freezing winter air temperature and frozen water surfaces.

In summary koi and all other pond fish subjected to very cold winter environments know what’s best for them… they sink to the bottom of the pond and become completely motionless.

This phenomenon of pond water having its maximum density at 4°C/39.2° F. (water above and below 4°C/39.2° F is of a lower density) is one of nature’s secrets to survival. Amazing isn’t it?

In summary a frozen pond will not result in the koi freezing to death even in very prolonged and cold weather (unless the pond is very shallow).

Pond Depth Is Important

By the way, this is a very good reason why most koi pond experts suggest that a koi fish pond should have a minimum depth of about 4 feet/1,2 meters.

During prolonged winter freezing conditions undesirable noxious gases remain dissolved in the water because they cannot escape through the fish pond surface as normal. Remember also that the processes of water purification (ammonia and nitrite removal) in the pond bio-filter should also slow down

It is therefore a good idea if prolonged freezing conditions are expected or encountered that a hole be maintained in the pond surface.

How to Stop a Fishpond or Koi Pond Freezing Completely…

Floating ice preventer There are simple low cost pond devices that allow a hole in the koi pond water ice surface to be maintained to allow these noxious gases to escape from pond water.

A pond de-icer is essential in some areas


These items use electricity but not all of the pond de-icer devices use electricity.

For those koi keepers who can afford it (and believe it or not many can) the ideal solution is to use an inline gas or oil fired heater to maintain the koi pond temperature at about 18°C/64.4° F.

Old  Fashioned Boiling Pot

If you can’t afford a pond de-icer of these then you can always resort to Peter May’s (A well known author) solution to creating a hole in the surface fishpond ice.

Boiling water for ice

Peter advocates the use of a saucepan containing boiling water. The saucepan is placed at a convenient point and the heat melts a hole in the frozen fish ponds surface ice so that pond gases can escape.

It’s a good idea to buy a low cost floating thermometer to monitor koi or fish pond water temperatures. And, by the way, if you don’t want to get in the pond and clear out the muck then consider a pond vacuum cleaner or pondvac for short. The pictures below are of a couple the Oase Pond Vacuum models but there are a few different kinds you can choose from very cheap to the very expensive. But the OASE Pondvac models are the best by far:

Here is a selection of Pond Vacuums
with prices to suit your pocket.


Can Koi Freeze?

I am often asked the question can koi fish freeze in frozen fish ponds and for that matter can goldfish freeze? Yes if you have extreme and very prolonged temperatures below water freezing point. This is highly unlikely to happen unless the fishpond is very shallow as I have mentioned above.

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