overwintering koi under thick ice

jennyb5149(3b)August 17, 2010

Hi everyone,

Hard to believe but the first hints of fall are already starting to rear their ugly heads up here in northern WI. BOO!!

So my mind has turned towards finding a home for the koi this winter. I know that for this coming winter I will be overwintering them in the garage in a stock tank. But, I really have been doing a lot of looking around and researching to figure out the best way to keep them in the pond year round as this seems like its a lot less stressful to the fish (no chasing them down and netting them) and less work for me!

I came across this article in Pond Trade Magazine on overwintering koi in very cold midwestern winters and wanted to get the reactions/feedback of all the more experienced koi keepers here.

Thanks! Jenny

Here is a link that might be useful: Overwintering koi under thick ice - article from Pond Trade Magazine

Thank you for reporting this comment. Undo

i'm in south eastern va. here people use a water troff heater the ones for cows water and air raters (i'm so not good at spelling) but the things that add oxogen and move the water bubbling on top to release gasses from the water. but i'm going to bring mine in this winter.

the article you found is great, thank you for sharing it.

    Bookmark   August 17, 2010 at 7:29PM
Thank you for reporting this comment. Undo

hello i found this article and thought it might also help you


    Bookmark   August 17, 2010 at 7:43PM
Thank you for reporting this comment. Undo
horton(6 b Ontario.)

Jenny, that is one of the best written articles that I have read about "wintering a pond".
The author, Jamie Beyer, has certainly covered most of the bases in a very informative way and has avoided re-quoting some of the myths connected to wintering a pond.

His advice about preparing the pond for winter, well before the cold weather sets in, is great advice. There is nothing worse than trying to make a vent hole in the ice when the wind and snow are blowing and the temperatures are numbing.

Two aeration pumps, as he suggests, are of course the best way to go. Even people who use electric heat pond de-icers, should consider having a back-up plan in place, just in case the heater stops working.

Never, never, never hammer on an ice covered pond to break a hole through after it is frozen over, as the shock-waves could damage the fishes hearing or even cause fish deaths.

I use a small water pump to keep a portion of my pond open and I also cover the pond over completely with a frame and translucent tarp. It keeps the wind from blowing over the water and locks in some heat from the sun. That may not be a practical plan for you in Zone 3.

I'm in Zone 5b and our winters can be harsh but we don't have the prolonged cold season that you encounter.

David (DRH) is away way up there in the frozen tundra of Vermont (Zone 4) and he has used an air pump and air stone in his pond over the winter, with great success for many years.
I even believe he has a similar system in the floor of his igloo so he can ice fish all season.:-)

I'm sure he will chip in with some very wise words of wisdom about over-wintering a pond. In fact David,Ronaye and Steve, submitted an article, some years ago, to the *FAQ on this pond forum, about this very subject.


* FAQ is at the top of the message posting page.

    Bookmark   August 17, 2010 at 8:05PM
Thank you for reporting this comment. Undo

I saved that article for reference for my climate. I tried 2 years in a row to overwinter fish in my pond with aeration but no heater. By the time January hit with our
-35C (sometimes -40C which is the same as -40F) the air dome had frozen over. Both times the fish were popsicles in the spring. Since the ice in my pond doesn't leave until mid April I bring my fish in every year. They are housed in a 300 gal tank in the basement and the water temp doesn't go below 70F so they don't get the "dormant" period the article talks about. I feed them all winter but only once a day and they are fine. There are people here who overwinter their koi in their ponds but they run aeration and 1500Watt stock tank heaters. Others have built a frame over their pond, plywood on top of that and straw bales on top of that--with aeration in the pond. I don't have access to straw bales and my pond is peanut shaped so kinda hard to build a frame over it. So I guess bottom line is either bring them in or experiment.

    Bookmark   August 17, 2010 at 8:34PM
Thank you for reporting this comment. Undo

Laura - thanks for the great article! I think that between the two articles I should be able to make something work!

Horton - As always, your advice is invaluable! Can't wait to see what you have to say about my pond expansion plans that I'm going to run by the forum later. Found a great seller of epdm on Craigslist that sells the stuff for .25 a square foot. Going to pick up a 18 x 19 piece on Saturday! Only $86!!!!

    Bookmark   August 18, 2010 at 11:03AM
Thank you for reporting this comment. Undo

I'm going to be digging a 4' x 5' addition to the pond this fall that will be about 6' deep. It will be connected to the main pond but will be separated in a way that I can block off the two sections. My eventual plan is to herd the koi (or more likely lure them with food) into the deep section for the winter and block off the entrance to the main pond.

I'm not sure if I should build some sort of green house over the section the koi will be wintering in or just let the snow do it's insulating effect. Unfortunately, the snowfall in the last few winters has been sparse. Last year we had probably 3' at one point but that is the largest amount we've had for years....most years it's been about 18" at any one time. northern ponders, any recommendations?

This winter will be the experimental stage. I'm going to go to PetSmart and buy some el cheapo koi to throw in there and see what happens. My pet koi are going into an insulated stock tank in my garage that will be aerated and have a homemade deicer in it (thanks Horton for pointing me to Greg Bickel's dvd!) I'll be back with a full report in the spring telling you how the experimental koi fared! :-)

    Bookmark   August 18, 2010 at 11:48AM
Thank you for reporting this comment. Undo

As Horton has mentioned, I live here in Northern Vermont - not as far north as some, but we get a bit of "cool weather" - typically down in the -20's. I've been wintering my Koi & Comets in our pond with nothing more than an aerator for many years with no loss other than a few of the Comets which get eaten by the larger Koi. The catch with this approach is that your pond must be deep enough. What is enough? It depends how deep the frost layer will penetrate the soil. Around here all buildings are designed with a minimum 4 foot deep frost wall. Our pond, however, is only a tad over 3 feet deep. Yet in all the winters we've been here I've not had frost penetrate much over two feet. The maximum ice thickness I've ever recorded is 18" but more typically around 12"-14" about 5 feet away from the aerator. According to what you've listed for your zone (3b) you may find the frost level penetrates significantly deeper unless you receive a fair amount of snow cover. Areas that only get 6" frost penetration can probably get by with an aerator and a 2 foot deep pond. By the way, if you do use an aerator do NOT walk out to the hole and check it!!! I can personally attest that the ice is very thin next to where the bubbles come up .... and the water is VERY cold! :-))

One thing not mentioned in the article/website you attached is location of the bubbler. I don't put it directly on the bottom of the pond but rather suspend it about 18" below the surface for two reasons: 1.)So I don't stir up anything on the bottom. The slow currents created with a suspended bubbler are sufficient to distribute oxygen evenly but without stirring up other "stuff". 2.)The amount of air from a bubbler/air pump is highly dependent on the back-pressure exerted on the pump or rather how much water depth the pump has to pump against. Some of these little pumps can only handle 2-3' of water head so if you had a fairly deep pond and placed the aerator at 5 feet or so you'd get no air coming out.

Plus the fact I really, really like the fact that my system only consumes 4.5 watts!!!!! My New England DNA won't let me hook up that 2500 watt tank heater!!!!
P.S. I think Horton lives down in the banana belt somewhere!!!

    Bookmark   August 18, 2010 at 11:41PM
Thank you for reporting this comment. Undo

Thanks David for the info! The author of the original article did address aerator depth in the comments section at the end in answer to a reader's question. He recommended putting the aerator all the way to the bottom. But, your rationale about keeping it suspended a bit off the bottom in order to stir up stuff makes sense. Even with the best cleaning I can give the bottom before the freeze up, I'm sure stuff will still be left behind in addition to other stuff finding its way in before the pond ices over.

I've put in an email to the local extension office to see if anyone can tell me what the average frost penetration is for my area. Hopefully that will give me some info on how deep is deep enough for the new pond addition. Since the snow has not been plentiful over the last several years, I'm not going to count on snow cover to add an insulating effect. I'd rather just make sure I get below the frost line from the get go.

I'm glad to hear that you've managed to over winter your fish with no problems. As I wrote in the comment section for the article I referenced, after spending more time in the past several winters than I care to remember freezing my *ss off sitting on the ice trying to catch fish, I knew that fish survive just fine in near freezing water and that, in fact, is the norm for them in the winters. So, I just couldn't understand why my koi couldn't do the same. Of course, they are a different breed of fish but even the very, very invasive asian flying carp are surviving just fine in the mighty Mississippi as far north as La Crosse, WI (about 50 miles south of Minneapolis/St. Paul). As an aside, everyone pray they never make their way into the Great Lakes...it will be devestating!

I know that other zone 3ers on here have not had any luck overwintering their fish so I'm gonna get all the best info I can when I build the new deep addition and trial it with some guinea pig fish this winter. Hopefully, if enough of us igloo-dwellers (you're in good company David!) can get our fish to survive the brutal winters, we can have some definitive recommendations that will help all the other crazy cold lovers like us help their fish make it through the winter.

    Bookmark   August 19, 2010 at 10:47AM
Thank you for reporting this comment. Undo
marn_eh(3 Quebec E.T.)

David, can I ask what brand of pump you use and where you store it when it's running over the winter? I live in a very cold climate (zone 3 because of my elevation) and I'm concerned about condensation freezing in the line. Has that been a problem for you?

Do you use a variation on the plastic bucket design in the link, or do you keep the pump in a shelter such as a garage?

My next question. What happens if the power goes out? We're in the woods and it's not unusual for a big storm to take down a branch and with it our power, too, every couple of winters or so.

My husband thinks that it would be necessary to have a check valve in the line near the airstone so that water wouldn't flow back into the line and freeze during a power outage. Do you have a check valve? Have you been through a power outage? How did you deal with it?

I'm thinking about getting fish next spring and trying the air bubbler solution to wintering them over. We can usually count on snow here and my pond is 4 feet deep, so I think I would have enough open water, even under heavy ice.

My husband and I are just trying to foresee and head off potential problems ... nothing like being able to share experiences from folks who've been there, done that.

    Bookmark   August 19, 2010 at 2:57PM
Thank you for reporting this comment. Undo

thanks for sharing a big help

    Bookmark   August 19, 2010 at 8:14PM
Thank you for reporting this comment. Undo

Jenny, I much prefer the cold to the heat! I've indicated a url below that should pop up a folder containing a pdf document for building a float - it's about the third document down in the list. There are also so couple of jpegs showing what it looks like. I've put this out here before and I know the data for the cost comparison is out of date but I believe it's all relative. The fundamental aspect was building a float which I could anchor in the middle of the pond to hold the aerator at a fixed spot and depth. The light bulb in a pot? Not sure it would work this far north.
Hi Marn! As to what type of air pump? I've been using Hagen Optima pumps - they're rated 4.5 watts, approximately 5 liters/min. Note that the air flowrate is "free air capacity" meaning no back pressure on the pump. Picked mine up at our local Pet Store (Petsmart) and have also ordered one through Amazon a year or two ago. They run about $38-$40 U.S. and you can get a kit for rebuilding one for around $2-$5. However, the exact type of pump doesn't matter too much...you want something with a little bit of umph behind it; something that moves 4 to 5 liters/min
As to enclosure...yes, you will want one. It can be nothing more than a rubbermaid tub turned upside down or a pail. In the document below I believe I described how I built one using slabs of foam insulation (left over from building the float - I bought the pink, 1 1/2" thick foam board - comes in 10 foot lengths so plenty left over to make a "pump box" or if you like you can use the blue foam board!). The foam board adds a bit of insulation to help keep the pump somewhat warmed. You do NOT want to put the pump in the garage or inside your house or any inside place!!!! What happens - very rapidly - is the pump sends out that warmish air. The warmish air is loaded with humidity which condenses in the air line and freezes solid. Usually only takes an hour or two to plug that way. By putting the "enclosure" - my foam box - out in the open - see jpegs in folder below - then the air pulled into the pump will already be at a dewpoint to avoid condensation in the line. I do not use or need a check valve since I make a point of keeping the pump & enclosure about 6" or so above the water level...no way for the water to back up into it. If I lose power and the water backs up into the line and freezes I've got a couple of options. The easy one - I keep a spare air stone and line handy or you can pour hot water on the air line to thaw it out.
The plastic film on the "teepee" structure - I tried using polyethylene on year but it broke down due over time. Best thing was when I was able to get the dry cleaner bags (they'll usually give you a couple for free!) which were made of the un-environmentally friendly stuff...but they would hold up for 3 years! May have to get some film they use for greenhouses this year - the UV stabilized material.
Feel free to contact me if you have any questions.

Here is a link that might be useful: Folder containing pictures and schematics

    Bookmark   August 19, 2010 at 10:23PM
Thank you for reporting this comment. Undo

Dr David,

Thank you so much for sharing your schematics and experience! I am feeling like I'm very well armed with plenty of info about helping my fish survive outdoors over the winter.

Just a few more questions before I go out and buy some guinea pigs - aka exeperimental fish - for the winter. I thought I'd ask the questions here on the forum so everyone can get the info. I figure if I have a question there is bound to be someone else out there who is wondering the same thing.

First, it sounds like from your posts that I shouldn't even bother wasting my time making one of the lightbulb deicers because they just don't do much in the northern zones when the really cold snaps hit. It seems like you've found that the aerators are sufficient to keep a hole open in the ice. Is that an accurate statement? And, what do you do when the really cold weather hits to keep the ice open? Is the aerator enough? The winters have been fairly mild here the last few winters but, it is still normal to get a really cold snap where the temps do not get above 0 degrees Farenheit (that includes during the daytime also) for about 10-14 days in mid to late January. Would I be wise to get a electricity guzzling stock tank heater to run during those few days? Like you, the thought of keeping that running all winter makes my New England DNA cringe! Well, I'm not from New England but I think I might have some in me because we both think alike on that matter! But, I could probably suck it up and put it on for the really cold, cold snap that always hits in January.

Second, does the plastic tent you designed to go over the air stone float prevent an ice dome from forming over the open hole in the ice? If it doesn't, at what temps (both daytime and overnight lows) do you recommend that I should be going outside and checking the hole for ice domes? And, if I do have ice domes, what is the best way to handle it? Poke holes? Splash some warm water? Does the tent need to be removed?

Okay I better stop with the questions for now and wait for a few answers. My mind is already starting to spin out of control with a bunch of possibilities and "what ifs"!

Are you starting to get some color in the maples in VT yet? First hints are showing up here already. Summers go so fast, don't they? Of course, what would life be if we didn't have snow shoveling to look forward to? LOL

Thanks again, Jenny

    Bookmark   August 20, 2010 at 2:54PM
Thank you for reporting this comment. Undo

Hi Jenny,
First, the more important questions: Nope, leaf peeper season hasn't started yet! That's usually the end of September - first week in October (for the Champlain Valley). Already many motels and Hotels are booked solid. Shoveling snow?? When one is retired it is irrelevant. You get up, you look out, you say "oh, it snowed last night; looks like 18". Isn't it pretty". You have another cup of tea/coffee; go back to bed or not. Wait until Spring to shovel out. Not-a-problem!

Now to your questions: First let's deal with some heresy: a hole in your ice DOES NOT MATTER! Gasp! WHAT DID HE SAY??? Nope, it's all about providing a surface for gas exchange. IF... you're using a heater, a light bulb, stock tank heater, etc. then it IS about keeping a hole open since that is the only surface over which the gas exchange can take place. However, with an aerator the gas exchange surface is in the bubbles...NOT in the hole that may or may not be in the ice. All that air you pump in there has to go somewhere otherwise you'd have the equivalent of one of those air-hockey games only with an "ice puck" floating on an air cushion! But that doesn't happen...the air finds a way out - through a crack, through the edges, though a hole. So if it "domes over"...so what? The air is STILL finding a way out. And because you are pumping air in it is the aggregate surface area of all those bubbles that is providing the surface area for gas exchange...and it is HUGE! With a stocktank heater in our neighborhood with our winters you might get a few square feet for a hole although at -20F you might find it disappears! But the aeration approach continues to put out 10's of square feet of surface area every minute!!! As a result not only will you keep more than enough oxygen in there (not really that much of a problem given that the metabolisms for the fish are almost non-existent as well as the microbes involved in consuming organics - and oxygen - aren't doing too much...but still not exactly zero!) but you will be stripping out ammonia and carbon dioxide and other gases you wouldn't want trapped under the ice. This is the real benefit of the approach to using aeration.

As to the plastic tent? Not sure it does too much although it does allow me to see the hole for an extra couple of months. But I've had it get ice inside, even an inch or so ABOVE the water level... but still not really relevant as long as the aerator/bubbler is doing it's thing. Note the ice auger in one picture...I went out to check one fine February day (think high of -10°F!). Couldn't really see a hole in the ice under the teepee. Drilled a hole and looked...yep, everything was working fine. But the ice melted out under the teepee more about a month before it melted out of the pond so there is some solar benefit. The real purpose of the floating thing is to hold the aerator above the bottom of the pond.

As to adding a stock tank heater on the coldest days?? I wouldn't bother. If you lived in zone 6 or 7 you might have some impact on the temperature in or around the heater but in my zone (and I suspect yours) adding even a 2500 watt heater is akin to performing a particular bodily function into the wind! Yes, it probably will melt out a hole, but once the heater is down near the bottom of the pond with an outside temperature of say -15° or -25°F I suspect there will be no measurable impact on water temperature. Having a heater on hand, however, does provide a way to work on thawing out a line if it develops an ice plug. I don't own a heater since, as mentioned above, I use other approaches for that problem.

Like I said.. it works for me and as posted in the URL above it works for other folks as well. The problem is to understand that you are not really trying to HEAT the water to some acceptable limit but rather maintain a surface area open for gas exchange. I like cheap. I like what works...and so far, over several years, it has worked for me. The biggest factor will be whether your pond depth and volume will provide the heat transfer necessary to keep a water layer below the ice, i.e., making sure the whole (no pun intended!) thing doesn't freeze up!

    Bookmark   August 20, 2010 at 5:55PM
Thank you for reporting this comment. Undo


My pond is about 3' deep and is only 150 or so gals. Like David I have some pretty cold weather up in the mountains.

I put my bubbler on an old birdbath stand with a garbage can inverted over it to protect it from the elements. Worked great all winter. Because I can't get to the pond once it snows, I never know how well it works, but so far the fish have been alive in the spring.

I used to cover the pond with a frame and plastic but one year the frame broke. Now I am using old windows from a pop-up camper that fit perfectly over the pond.

The link below will take you to pictures I posted in a thread about bubblers a couple of years ago.

    Bookmark   August 21, 2010 at 6:26PM
Thank you for reporting this comment. Undo

Thanks David, Horton and everyone else who contributed to this thread!

Okay, I think I'm about 95% confident I can get my fish through the winter. Still debating whether or not I should try this winter or not. I read somewhere - I think on Greg Bickal's site that koi should be at least spawning age before attempting to overwinter outdoors.

I'll keep you all posted on the fate of my fish! The maples have officially started changing colors and fall is definitely in the air so I will know soon. thanks again!!! :-)

    Bookmark   August 24, 2010 at 3:28PM
Thank you for reporting this comment. Undo

HI everyone,

If anyone is interested I tried to overwinter my koi this past winter using Doc David's advice posted on this thread and here is what has happened.

All the stars finally lined up today: the pond opened up AND it was light enough after work to put the AquaVu down in the pond and see what was going on 6 feet down.

In case anyone is wondering an AquaVu is an underwater fish camera marketed to anglers. Anyway, got the bf out there with his AquaVu to see if anything was living in the pond. Along with a bumper crop of string algae already blooming we managed to find 2 live koi swimming around.

I started the winter with 6 koi and 2 shubunkins. My bf speculated the koi were spooked by his camera and probably all of them are still alive down there; we just couldn't see them because they were swimming away from the camera. He looked carefully for any dead fish carcasses on the bottom and couldn't find any nor were any floating on the top.

Soooo...SUCCESS!!! I'm really excited especially since we had over 10 consecutive days of below zero weather in January.

I'll come back and let you know the final fish count once the water warms up and the fish start getting active enough that I can see them without the aid of an underwater camera.


PS Thanks Doctor David!!! Worked like a charm!

    Bookmark   March 16, 2011 at 8:41PM
Thank you for reporting this comment. Undo

I have overwintered my koi for 5 years now pond is 3.5 ft deep at deepest point . I use a bubbler ,the ice is gone and their starting to get active i have never lost one.

    Bookmark   March 17, 2011 at 4:07PM
Sign Up to comment
More Discussions
Growing store bought lotus?
I found lotus roots in the grocery store tonight. Maybe...
Tropical marginals dormancy
Two months ago I planted an Umbrella Palm and a Papyrus...
Pond Heat
What is the best method of heating water to 70 degrees...
A deck window to my pond
Covered a portion of my pond with a deck so I decided...
People viewed this after searching for:
© 2015 Houzz Inc. Houzz® The new way to design your home™