Pond frozen over
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.

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. 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.

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 in a fish pond 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.

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. 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).

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 floating 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.

If you can’t afford one of these (see links and images above) then you can always resort to Peter May’s solution to creating a hole in the surface fishpond ice. Peter May is a a well-known author of Water Gardening books from the UK.

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 fish pond 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.

You can even monitor your pond temperature from your armchair using this clever pond temperature device:-

41S9NvWtGXL. SL160  - Frozen Fish Ponds
See larger image
Additional Images:410pftUws2L. SL75  - Frozen Fish Ponds
31qBM66JrmL. SL75  - Frozen Fish Ponds
41t0dAAsngL. SL75  - Frozen Fish Ponds
31oKBuNWMZL. SL75  - Frozen Fish Ponds

SensorPush Wireless Thermometer/Hygrometer for iPhone/Android – Humidity & Temperature Smart Sensor with Alerts. Developed and Supported in The USA (Kitchen)


  • Flexible: Add a SensorPush G1 WiFi Gateway (sold separately) for data and alerts via the Internet
  • Powerful: Line of sight range of 325 feet keeps you up to date, even on the other side of your home
  • Easy one-time setup with our beautifully designed, free app (iOS or Android)
  • Accurate: Swiss-made sensing component provides reliable, accurate measurements
  • Set it and forget it: Pushes readings to devices via Bluetooth and alerts you if there’s a problem

New From: $49.99 In Stock

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 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 but also the most expensive:

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

41HraOCfx5L. SL160  - Frozen Fish Ponds
See larger image
Additional Images:51Fc0No1G8L. SL75  - Frozen Fish Ponds
61diLkojkFL. SL75  - Frozen Fish Ponds
51XMn+Cgx6L. SL75  - Frozen Fish Ponds
61wRqKMkfRS. SL75  - Frozen Fish Ponds

OASE 48080 32270 Pondovac 5-Dual Pump, Brown/A (Lawn & Patio)


  • Suction and drainage pumps run Simultaneously for continuous, uninterrupted suction
  • Maximum suction flow Rate of 2100GPH and maximum suction depth of 7.5′
  • Regulator on handle allows flow adjustment, and larger wheels stabilize vacuum movement
  • Includes 4 aluminum suction tubes, 1 transparent suction tube, 16′ Suction hose, 32.8′ Discharge hose with quick connect fitting
  • Includes 5 nozzles: Adjustable floor nozzle, string algae nozzle, wide nozzle, brush nozzle, wet suction nozzle

New From: $739.99 In Stock

Can Koi Freeze?

I am often asked the question can koi fish freeze 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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