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Robyn's Winterizing Page

Last Updated: 8/8/21

Ice covered large pond topped with four inches of snow, 1/8/99.

Note: My pond is in Zone 6/7. While I try to cover information valuable to ponders in all zones, this page is most helpful to those in areas with low temperatures of -10 to 30 degrees F.

Pond Winterizing

Keeping the Pond from Freezing Solid

De-icer Tips

Seasonal Care

Videos of Robyn's Pond in Winter

Winterizing and Seasonal Web Sites

Winterizing Information on Other of Robyn's Pages:

Winter Pond Photos
Old Videos of Robyn's Pond in Winter
Helping Frogs and Toads to Overwinter
Overwintering Frogs and Toads Indoors
Turtle Ponds in Winter
Overwintering Tropical Lilies
Discussions of My Seasonal Chores and Overwintering Information on My Pond Newsletters
Indoor Ponds
Ponds During Snow and Blizzards
Short Article - a piece I wrote on overwintering pond plants and overwintering aquatic frogs indoors for Organic Gardening up on their site. Of course, like all web pages but mine, it is gone now so I removed the link. And, they blocked archive.org from archiving it. I tried to find the article in my files but all I found was a Galley for a longer article I wrote for them.


The key to a successful winter is to keep the pond from freezing solid. The pond should also be at least a foot deeper than the ice line would ever be in your area if you are keeping small to medium fish like goldfish and minnows. If you are keeping large koi or other medium to large fish, then at least two feet below the maximum ice depth would be needed to provide the fish with room to move (for large koi, an ideal pond in Zone 6/7 is 4 to 7 feet deep). To keep an open area, you can use aerators, de-icers, or the pump. I use a de-icer over the pump and leave my pump and waterfall going over the winter. In small ponds and often in big ponds, it is best to put up the pump for winter. If it freezes, it could be destroyed. Freezing waterfalls can also divert the water out of the pond and pump the pond dry. In this case, providing aeration with a Luft pump or using a de-icer becomes even more important.

Go to Robyn's Winter Pond Pictures Page to see winter photos of Robyn's 1800 and 153 gallon ponds! I moved that section out of this page to save room.

Information on what to do in the winter (and any time of the year) during a power outage, can be found at my pond care page.


The pros and cons of removing pumps:
Some people believe in keeping pumps in during winter and some believe they should come out. The reasons to take it out include preventing possible destruction of the pump through freezing (especially if power fails and restarts), prevention of plumbing freezing, reducing disturbing the fish through motion, saving money on electricity, prevention of mixing possible temperature gradients, prevention of further cooling of the pond due to evaporation (water/air contact), prevention of ice dams which result in pumping out the pond, etc. Reasons to keep it in include helping to keep the pond from freezing, reducing stagnation on warmer days, getting a jump on building up nitrifying bacteria in late winter or spring, continuing filtration, preventing the death of any plants like watercress in the waterfall or stream, aeration (important when the pond is overstocked), etc.

My opinion based on my experiences:
Flowing water will not freeze if it moves fast enough (this will not work with slow waterfalls in really cold weather). If you keep the pump in, put it near the surface but below ice. Keeping a pond de-icer near the intake helps. Burying tubing should reduce its chances of freezing. Providing lots of pots, rocks, etc. in which fish, etc. can take refuge reduces the effects of water motion disturbing the fish. In small ponds less than about three feet deep, the temperature gradient is negligible. While my waterfall does cause some further cooling of my pond, I believe the advantages (keeping the watercress alive, keeping the pond filtered and the bio-filter ready for spring, aerating the pond, etc.) outweigh this problem. If the waterfall or other moving water is left running through the winter, the pond will require frequent additions of water as the evaporation rates can be just as high as in summer.

In December of 2000, the weather was extreme here in MD in Zone 6/7. The pond was frozen solid except at the de-icer and parts of the waterfall for a month before it warmed up. Ice formed over a lot of the waterfall. I had to constantly remove ice (in other words, beat it with my aluminum net pole which I totally annihilated) from the waterfall to keep it from diverting and pumping the pond out on top of the ice. Someone in the next county pumped out their entire new pond (luckily there were no fish) when the waterfall froze and diverted. I came pretty close to turning off the pump but am glad I did not because it got warm in January, and the fish need the aeration. Like most ponders, I have way too many fish!

My suggestions:
I suggest removing the pump in Zones 5 or less, in ponds under 500 gallons (prone to freeze pump), or if you so choose. Each situation is different. It depends on your pond's volume, location, plumbing situation, and year-to-year extremes in weather. In warmer areas or larger ponds, there should not be a problem leaving the pump in the pond. Extra pumps, filters, UV sterilizers, carbon, ornaments, etc. should be brought inside for the winter. A pre-filter and bio-materials (lava rock, etc.) can be left in as long as they do not impede the flow when left dirty through an entire winter. Outflows can be re-directed to just churn up the water instead of going down the waterfall if you wish. I think water running down a waterfall surrounded by snow is very pretty. However, when it gets really cold, and I dash outside in 10 degree F weather at 2 am (because I had a nightmare that the biofilter froze and the pond pumped out all the pond water), and I put my bare hands in the filter to pull out the ice, I wish I had just turned it off. Of course, the next week, it is up to 50 degrees F, and I am glad I left it running.

Pump storage:
Most pond pumps (Mag Drives, etc.) of today can be stored dry. A few older or complex pumps may need to be stored wet. It is best to use deionized or distilled water but tap water is okay in most cases. Pumps that contain oil may require maintenance and/or oil changes. If possible, the blades on any pump going into storage should be checked and cleaned of debris. Many pumps today are encapsulated so that no maintenance is needed or possible.


The plants section is now on my overwintering plants page.


You can either bring the hardy fish (goldfish, koi, orfe, minnows, mosquito fish, etc.) inside or keep them in the pond. If you bring them in, do it once the temperature goes down to an average of 55 degrees F or less. Stop feeding overwintering fish at this temperature. They will become less active and spend more and more time on the bottom. The fish will go into a sort of hibernation over winter. If there is an adequate size opening in the ice for air exchange, most of the fish should make it through winter. Weaker, young, old, small, and large fish are most likely to die. Remove their bodies as soon as you see them to prevent pollution of the water. Do not mistake fish resting in a stupor on the bottom for dead fish. Dead fish can be anywhere in the water column and in any position. They often look washed out. Any tropical fish must be brought in before the pond goes below about 60 degrees F. Tropical fish are easy to take care of inside. The main disadvantage of bringing goldfish, koi, and orfe inside is that they need huge tanks and require a lot of time for care while inside. Large fish do not do well when kept in aquariums over winter simply because they do not have enough room, and the water is hard to keep clean and safe without intense filtration.


Information on frogs in winter can be found on my amphibian wintering page.

Keeping the Pond from Freezing Solid

One of the most important things to remember about winter is to keep the pond surface from freezing solid. This allows air exchange between the pond and air. If the pond freezes solid and there are too many animals under the ice, carbon dioxide will build up in the pond and oxygen will become depleted. Then, any animals in the water under the ice can suffocate. [Some people say natural ponds freeze solid, and the fish are fine. That is somewhat true but our ornamental ponds are most likely way overloaded with fish and other animals. Natural ponds are large and rarely freeze solid for long. Also, while clay and dirt ponds can "breathe", EPDM, PVC, etc. will not allow any air exchange.] There are a number of ways to keep a hole in the ice which are listed below. The first four are most common. The other methods are for areas either without electrical supplies (or during power outages) or for ponders with limited resources.

1. De-icers:
A 1250 W, 1500 W, or similar heated de-icer will keep a hole in the ice. It only comes on when the water is near freezing. De-icers cost about $20-$40 initially but most increase the electrical bill (sometimes a lot!).

2. Heaters:
Heaters are usually reserved for koi keepers who keep the entire pond heated to 40 or 50 degrees F during the winter. Usually the water is circulated through a gas heater (natural gas if available or propane) and then that water is added directly to the pond or run through piping under the pond floor. These systems require lots of money initially and for continual heating. A new pond heating system that costs a few hundred dollars and uses sunlight to warm the pond instead of electricity or petroleum products can be found at Aquatill.com. It may not prevent a pond from freezing in winter but can warm the pond during the cooler days of spring and fall.

3. Pumps:
Pumps create moving water. Moving water rarely freezes. In the colder areas, the pump can be placed about a foot below the surface and water is not pumped anywhere but just squirts up out of the pump like a fat fountain. In warmer areas, the pump can continue to run filters and/or waterfalls (fountains are not a great idea unless in Zone 9 or higher which are the warm areas.).

4. Air pumps:
Air pumps (usually the Tetra Luft pump in the USA) can be used to maintain an open area as well as aerate the water. This is cheaper than the above three methods. Place an air stone about 6-12 inches down into the water. This creates water movement keeping a small area from freezing.
Note: The Tetra Luft pump is a must-have pond supply but they no longer make it (or so I was told)! There are very expensive ($300+) larger aeration systems that are just too big for ornamental ponds but good for farm, deep koi ponds, and other large ponds (sold by Pond Guy, Aquatic Ecosystems, and other places.). One possible replacement for this system might be the OASE pond-air aeration pump which costs about $53 in 2002. Two places that sold it were Aqua-Mart and Drs. Foster and Smith. Aqua-mart is now AAA Pond Supply, and while they no longer have that aerator, they do have other aerators available. Here is a photo and link to purchase the OASE air pump at Drs. Foster and Smith. Next to that are some other aeration kits.
Drs. Foster & Smith deleted their affiliate program so these links will no longer work. I am leaving up the pictures which are still working for now.

I got one of the OASE air pumps, and it is not what I thought. It sucks air off the surface and mixes it in the pump and spews it out. It does not look like it would work in freezing temperatures but I will use mine to add oxygen to my large pond in summer only. I used it for one year, and it died. Guess what! Now, I see that Drs. Foster and Smith carries the Luft pump in their aquarium catalog! It does not contain the outdoor cover but it looks like the same one! You could cover it with a plastic storage box or something. I bought one on 1/25/05, and it is not a Tetra Luft pump; it is a Coralife Luft pump but it looks like it could still be used the same way. Here is a link to it on Drs. Foster and Smith.
Drs. Foster & Smith deleted their affiliate program so these links will no longer work. I am leaving up the pictures which are still working for now.

5. Floating styrofoam, black disks, or small domes:
There are a few products that are sold that are supposed to keep a hole in the ice without electricity. These include a white styrofoam thing with a tube down the center. While it is supposed to work with or without aeration, this may not work for really cold nights. There are also various black disks and plastic domes that people swear by. I have never tried these. Sometimes the plans to make these show up in the pond magazines. If you need plans, try asking at the newsgroup rec.ponds.

6. Boiling water:
If despite any of these above methods or due to a power outage, the pond freezes solid, a hole needs to be opened. Banging on the ice or using a hammer can cause shock and stress to the fish in small ponds and should not be done. Stepping on the ice is not as bad. Then, sheets can be removed. Boiling water is the best way to open a hole. Obviously, this method would not work to keep the pond continuously open unless you had nothing to do but boil water all day. It will help if the power is out or to open a hole at least once a day to let out trapped gases if nothing else works. Of course, if the ice is thick enough and it is cold enough, even with boiling water a hole may not open. I am not sure what you would do then. Elaine in Zone 2 uses an electric ice saw. Others have suggested ice augers.

7. Water removal:
In very large ponds in Zones 4 to 7 or so, the following may work. Let the pond freeze solid to at least two inches. When this occurs depends on the location. Then, melt a hole in the ice with boiling water or use an ice cutter. Then, drain (pump or gravity) the pond down a few inches so that there is a gap of about 2 inches of air between the ice and the water. This only works if the ice is frozen enough so that it will not collapse. So, it would have to be at least two inches thick. This only works on huge ponds. Most likely, a water gardener would not use this approach except perhaps on a much smaller scale in ponds of at least 1000 gallons (lower the water to say half an inch below the ice). This would be more for a farmer's fishing pond. The gap of air allows some air exchange between the water and the gap. The ice and air help to insulate the unfrozen water below. Just do not go skating on the pond after this! I would not use this method but I want to provide all of the known options for you to peruse.

8. Domes or green houses:
Some pond keepers erect domes or green houses over their ponds in winter to warm them. These work well in places with cold and windy winters to keep the pond warmer. One such pond can be seen at this site.

9. Salt:
This will not keep the pond open but it does help a little, mostly to dissolve up ice accumulations. On 1/24/03, my 1800 gallon pond was very close to freezing so badly I would have to turn off the waterfall. Only a little was open. The falls built up a large ice mountain where they spilled. I pulled out my pond salt early. I normally add it in spring. I put about 5 pounds in the water and sprinkled it around. Where I threw some on the ice mountain, a few days later there were little holes in it. The salt helped break up the ice and perhaps lowered the freezing point (not really significantly but it is something at least!). Be sure to only use pond or aquarium salt or pure sodium chloride and do not exceed a concentration of 0.1 % in the pond (see my health page for the benefits of low salt levels for fish).

10. Brooder Lamp and Aquarium Heater:
On 8/13/04, Steve in Kentucky sent me these ideas for small ponds. I do not know that I would use it but perhaps someone else may find the need.
"...I have goldfish in a smaller preformed pond. In the winter, I move it under the cabana and hang a brooder lamp about 2-3 feet over it. It actually keeps the water warm enough that the fish continue to eat all year. Sometimes I get an algae problem; sometimes I don't. I've done it out in the open, but if the rain blows under the reflector, the bulb explodes. Another little trick is to take an aquarium heater rated for the gallons of the pond (works well with small ponds) and suspend it from a broom stick or similar in the middle. It keeps a place about 1 foot in diameter de-iced and I've recorded January temps in the 60's near it. If the fish want to, they can swim to the colder regions, or stay in the warm zone."

De-Icer Tips

For my two largest ponds, I use 1250 W de-icers from Farm Innovators, Model P-418. I let my other ponds freeze solid (after removing all animals for the winter). Here is a link to the kind of de-icers I have. Drs. Foster & Smith deleted their affiliate program so these links will no longer work. I am leaving up the pictures which are still working for now.

Here are a few tips on using de-icers.

1. If you keep a pump and/or filter going during the winter, set the de-icer over the pump intake to keep it free of ice.
2. Try to place the de-icer over the deepest portion of the pond and out of prevailing winds.
3. If after high winds, the de-icer freezes solid into the ice, it may mean that the thermostat is confused and needs to be reset (or it is dead!). The advise is to remove the de-icer from the pond and place it in the freezer for a few hours before putting it back into the pond. When my de-icers (a year-old one and one new one only in the pond a week) froze in, I tried just unplugging for a few hours and re-plugging but that did not work. I then used hot water to pull the heating element out of the pond and let is sit, unplugged, for a few hours. When plugged back in, that did not work either. I put my spare de-icer in my big pond in the mean time. The cords were frozen under 4 inches of ice (1/17/01) but after they thawed, I tried the freezer trick to see if it works. Well I tried putting my two month old de-icer in the freezer for many hours and then back into the pond. It did not work! The outlet works (I checked with a radio) but both de-icers freezes in when it is cold. I bought a brand new de-icer for the big pond which works. I had to order another for the smaller pond. I finally talked to the manufacturer who told me to put them in the freezer again. After an hour in the freezer, when plugged in inside the house dry, all three of my "dead" de-icers clicked after two seconds and got hot after a few more seconds. So, apparently they work but still freeze when in the pond because the wind or something confuses the thermostats over and over again.
4. If the de-icer accumulates deposits on the metal underside, it is usually due to salt in the pond. Use a stiff brush to clean it off when you take in the de-icers in the spring and during the winter if the de-icer appears to be failing.
5. ALWAYS KEEP A SPARE DE-ICER! My de-icers only last about a year due to the low levels of salt in my ponds that eat up the heating element. If you do not keep a spare and your de-icer quits, I guarantee you that all the stores will be out of stock when you need a de-icer the most.

Seasonal Care


Winter is the time to relax and plan you next pond. The pond plants and animals will be resting and require almost no care. You just have to keep the pond from freezing solid. This is the time of year that I am afraid to go check on the pond because I might find that it froze or the biofilter froze and the pump emptied the pond. I could also slip on the ice or snow. In the winter of 1999, I was able to stand in the pond, in the shallow end, on top of the ice which is a strange feeling. See winterizing above on how to prepare for and deal with winter.

Winter Tasks:


Spring is the busiest pond season. All of the ornaments, filters, pumps, plants, and animals brought in for the winter go back outside. This is the time for ponders to clean the pond. See cleaning the pond. This is the time to repot plants (I hate that). See repotting on my plant page. New fish, tadpoles, plants, and other critters are best purchased in late spring. To help biofilters get started in early spring, add bacteria. See filtering for more information on biofiltration.

Spring Tasks:


Summer is the time to enjoy the pond. All the plants and fish will be at their peak, growing and reproducing. Flowers and babies abound. Continue feeding, cleaning, and adding new plants and/or animals. Refer to all my other pond plant and animal pages for their care.

Summer Tasks:

How to keep ponds cool in summer:
Ponds that are larger and deeper are cooler in the heat of summer. It is important to provide depth to ponds in hot areas to keep them cooler. Also, adding lots of plant cover such as water lilies, floating plants, and submerged plants will keep a pond cooler. An arbor can be built over a pond and covered with a tarp to block out some of the sun and keep a pond cooler. To keep small ponds cool, besides keeping them in the shade and adding lots of plants, you can also add cool water daily. Small ponds can also be cooled by floating ziploc bags of ice on the pond or removing some of the hot and replacing with cold water. Do not cool the pond too much as this can shock the fish.


The pond is at its healthiest in the fall. The water is the most clear at this time. Give the pond a good vacuuming or cleaning in early fall. Start bringing in ornaments, tropical plants and animals, and filters and pumps for the winter. See winterizing above for more information.

Leaf Nets and Skimmers:
Put a net over the pond if leaves will fall in it. An alternative is a leaf skimmer which are usually only installed on koi ponds (they also suck in small fish and floating plants that non-koi ponds want to have). Leave the net on until all the leaves are off the tree and collected off the ground from the immediate pond area. While some leaves provide cover and food for pond animals, excessive leaves will cause the pond to have an overload of organic material. In the fall, leaves may tint the water brown or yellow from the tannins which also may decrease the pH. In the spring, the leaf litter translates into a massive algal bloom and perhaps dead fish as well as a dirty looking pond. So, if you are not striving for the all natural pond and have deciduous trees, then a leaf net or a skimmer is a must.

Leaf Removal Hint:
We found a great way to get leaves off the huge leaf net on our 1800 gallon pond. Instead of grabbing for them and risking falling in or trying to use a grabber or net to get one or two leaves at a time, we use a wet/dry shop vacuum to suck up leaves off the net and rocks. It saves a lot of time and makes it easy to remove leaves far out on the net.

Fall Tasks:

Videos of Robyn's Pond in Winter

Winter pond photos are on this page. Here are the newer videos on You Tube:

Frozen 1800 gallon pond on 1/23/13.

Frozen 1800 gallon pond on 1/23/13 and how I use the sledgehammer on the waterfall ice (not the main pond).

Older pond videos in the winter can be seen on this page.

Winterizing and Seasonal Web Sites

Dan's Winterizing Page - includes information and links to other pond winterization web sites

Winterizing Water Plants, Fish and Ponds - an article on winterizing mostly plants. I do not agree with everything they say. For example, hardy lilies are hardy in most areas. As long as their roots do not freeze, they have a good chance of surviving winter. This site may no longer exist even though I was just there, if you know what has happened to it, please e-mail me.

Winterizing Questions - a site with a series of questions and answers. While there is some useful and interesting information, I found some of the site confusing. For example, it talks about water hyacinth and water lettuce dropping seeds in ponds in areas as cold as Zone 5 and having them sprout. I have never had water hyacinth sprout (but it may), and while water lettuce can produce tiny flowers (I have never had them), I do not know of anyone who has had them sprout either.

Koi Dome - one pond keeper's website which includes photos of the dome they erected over their koi pond so that they can enjoy active fish, blooming lilies, and picnics in winter in Zone 5/6.

Aquatill.com - sells a new system that heats ponds in cool (but maybe not freezing) weather using sunlight by putting a large black sheet over a fence or on a roof that conveys heat to the pond, costs a few hundred dollars but no electricity required.

Pond Winterization - article at About.com which also includes some links

Winterizing Your Pond - from an Aquascape builder. They recommend the "do nothing" approach.

Seasonal Pond Care from The Water Garden (a store). This page covers winterizing mostly but also spring information.

Theo's Pond Heating System

Winter and Summer Fish Kills in Large Ponds

Winter Care Guide for Garden Ponds

Preparing Your Pond for Fall & Winter

How Turtles Overwinter Under Water

Portable Pond Covers - tents for ponds

Pet Link Banner Exchange:

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