By: Mike Gannon | Posted On: January 25th, 2010 | 28 Comments on THE FROZEN POND | In: KOI PONDS, POND MAINTENANCE, WATER GARDENS

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    Frozen ponds is a subject that of course only seems to pop up seasonally, like during winter…well of course, why worry about it at any other time of year? The problem I see again and again with many pond owners is a real misunderstanding of what is happening with their ponds during this season, and if the subject is not addressed quickly the season ends and if a pond is not frozen why talk about it. So NOW is the perfect time. Here in the northeast U.S. I’d guess just about everyone’s ponds are frozen if they have not taken the steps to de-ice their ponds. So, naturally this is the time everyone goes into panic mode about what to do with their iced over pond.

     Here is some, I hope, comforting information about frozen backyard fish ponds and watergardens. When a pond freezes over it forms what would best be described as an ice cap. This ice cap will generally extend from edge to edge of the pond, but it is not airtight and will still allow air flow. This seasonal stage of your pond can be very pretty and enjoyable IF you truly understand what is happening below that ice cap that is putting a barrier between you and your fish and plants.

     The primary customer concern with freezing ponds is how the fish that are below that ice cap are dealing with it. I have yet to get a distress phone call from a customer about how the ice is affecting their water lily, after 15+ years in the pond industry that phone call has not yet come. The distress phone calls are always about how the ice is affecting the fish. On the assumption that your pond is: an in-ground pond, constructed properly to a depth of 30+ inches, and fairly well managed during the year and is not ice capped with loads of decaying leaves, debris, or putrefied food below it, the following information will apply.

     Ponds freeze from the top down and RARELY freeze solid all the way through. Fish ABSOLUTELY DO NOT under any circumstances freeze into the ice and then thaw out during the spring to comeback to life. If a fish freezes it only has one outcome…death. I have customers swear their fish are frozen into the ice, but I personally assure all of you and them this is not the case. When you see a frozen pond it is only ice capped which will slow down the oxygen intake and ammonia release of the pond, but it does not stop it. In many ways a winter time ice cap for your pond is desirable. The ice cap on the pond does not actually even touch the water, and really acts as a fantastic form of protection from the harsh conditions of winter. Between the water and the ice is a pocket of air and below the air pocket is fresh unfrozen oxygen rich water. Very cold water carries large amounts of oxygen which our pond fish utilize during the frozen times and our aquatic plants still photosynthesize during the winter and create more oxygen for the fish.

     Do not EVER try to walk on your frozen pond for the obvious safety reasons. It is a good idea, however; to keep the pond cleared off of snow, try to use a long handled broom to clear snow as the noise of shoveling can be a bit much for the dormant fish. We still want to let light into the pond for our aquatic plants to do what they need to do, create oxygen. Breaking a hole in the ice is not a good idea as it stresses the fish, try quietly melting a hole in the ice if you need to. Recent studies do relate that the amount of oxygen that diffuses into pond water during the winter is very minimal, so those de-icers and aerators we all hook up are doing more of a job of degassing the pond of ammonia build up, rather than oxygenating a pond and quite honestly the floating de-icers really don’t do too much at all. Studies have actually proven that ponds that are ice capped and have dormant aquatic plants will have a rise in oxygen levels if left undisturbed. The stirring or circulating of an ice capped ponds water is not really a good thing to do, unless it is a very dirty pond and an emergency situation is on hand, otherwise leave the pond water alone and let nature do her thing.

Have A Question For Mike? Ask the Expert

     Pond aerators should be employed and placed into areas that maybe “dead zones” during the rest of the season. Aerators should keep an open area most of the time but even when they get frozen over and you have an “ice dome” those aerators are still degassing the pond and moving that pocket of air in between the pond water and the ice cap.

     Fish will remain dormant, or in stupor mode, during this time and many fish experts agree that this dormant period, for koi especially, is important and koi have evolved to endure these conditions. At the end of winter when spring returns and we can start so see our fish again, the will surely be a bit thinner but that is normal and shows that they were able to handle the winter time and utilized the fat reserves they build up in preparation for the cold spells. It also gives you the opportunity to enjoy feeding them and getting nice and rotund again during the rest of the season.

     Frozen ice capped ponds should be as relaxing to look at as your pond is at any other time of the year and hopefully with some of this information you can now rest easy and know that your fish will come through winter after winter without any issues. Keep nutrient load low, keep fish population controlled, provide a simple aerator, and don’t mess too much with your pond and you and your pond will be fine. It is a short seasonal period of  freezing, enjoy the short lived beauty of an iced over pond because the spring will be here before you know it!

Written by Mike Gannon

Mike Gannon

The LOVEYOURPOND Blog is written by Mike Gannon of Full Service Aquatics located in Summit, NJ. Mike is an award winning pond, water garden, and water feature builder. Always “In The Pursuit Of All Things Aquatic” Mike has been a lifelong hobbyist and providing professional services since 1995. Mike is the creator of The Pond Hunter video series seen on Youtube and has made several television appearances on Networks such as HGTV and the DIY Network. He also hosts the Pond Hunter Radio Broadcast, a show on everything aquatic, every other Wednesday at 8pm EST. You can see what else Mike is up to at the following sites:

    28 Comments on THE FROZEN POND

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  1. Jen Says:

    on February 1, 2010 at 10:46 am

    Great blog entry! This helps me be more comfortable with using my aerator as my de-icer which is a huge weight off my shoulders (and wallet!), THANKS!

  2. bob Says:

    on May 2, 2010 at 10:17 pm

    I love all these self proclaimed aquatic experts. If you stayed awake during High School chemistry you would have learned Boyle’s law and would never make the inane statement that gasses wont diffuse into water at low temperatures. So much for the internet “experts”. Isn’t there anyone in the pond business that actually knows what they are talking about?

  3. Mgannon Says:

    on May 3, 2010 at 8:55 am

    Hey Clueless, great name! I am not seeing where it was stated that “gasses won’t diffuse into water at low temperatures” in my blog post. Maybe before your start an angry rant you should make sure that your ranting at least has a basis to support your negative and incorrect criticism. THINK before your post these ridiculous rantings, and make absurd conclusions about peoples high school education that you know absolutely nothing about. High school was a long time ago for me, maybe you should move on too.

  4. Vrina Says:

    on March 18, 2011 at 8:39 am

    I live in upper New York. My 2 ponds are not huge or probably more than 24 to 30 inches deep. Each year as it gets cold I don the old wader boots, take out all my filters and pumps, clean and put back in ponds. I leave the pumps right below water level to keep small opening in ice when ponds freeze over. My fish all fare well and seem fine come spring. All my water lillies come back also.

  5. Mgannon Says:

    on March 22, 2011 at 2:12 pm

    Hey thanks for commenting! I am glad that your ponds do well each year. obviously you’re doing something right! I’d love to see some pictures. Visit me on Facebook too.

  6. Cheryl Says:

    on February 22, 2013 at 4:27 pm

    I was wondering how long a pond can remain frozen over before it affects the fish? I read somewhere not to let it stay frozen over for more than 2 days. Year after year here in the northeast my pond at some point will freeze over and Im afraid to even let it close up at all. I currently use a pond heater along with acerator and the pond is 30″ + deep. Thanks much

  7. Mgannon Says:

    on March 2, 2013 at 4:00 pm

    Hi Cheryl, most ponds can stay frozen over for longer periods of time, but it is depending on the condition of the pond. If the pond was not well maintained it will be more of a risk. Also you should have an aerator and/or de-icer set up on your pond int he colder regions to make sure that there is an exchange of gases in and out of the pond. Looks like how you are set up should not be a problem if your pond is covered for extended periods of time. Thanks for reading and commenting, I love hearing from readers!

  8. Norm Says:

    on December 20, 2013 at 1:11 am

    I just came across your blog because I Goggled covered ponds. I have had a pond for 10+ years increasing it in size several times. It has a max depth of 28 inches. I have only lost my fish one time over the winter as the liner failed and the water drained out under the ice cap. I have always kept a hole in the ice to release gases. This year I decided to cover my pond using PVC pipe, insulating foam board, and plastic sheeting. I also put in air stones to increase the oxygen content of the water. I monitor the undercover temperature and the water temperature remotely. I live west of Chicago and after a few 0 degree days my pond is not frozen. The coldest the under cover temperature has been is 31.4 degrees and 37.9 degrees for the water. If this works out I plan to cover the pond again next year but make it high enough to stand under.

  9. Virginia Says:

    on February 12, 2014 at 7:37 pm

    What reassuring information! I have a 1500 gallon pond that is 3 seasons old. I am used to my koi wintering over during the winter months. But I’ve never experienced ice! I live in Atlanta and we are experiencing an ice storm right now. Power outages are inevitable. I’m worried that if our power goes out, my pump, aerators, filters, etc will stop as well. Right now, the pond has not frozen over because the water is flowing down the waterfall. I assume it will freeze if the power goes out. Instead of worrying, I will do as you say and enjoy the beauty of it knowing full well that my koi are okay. Thanks so much for your blog! VA

  10. Mgannon Says:

    on February 13, 2014 at 12:28 am

    Hey Virginia, I’m glad this was of help. Good luck with that nasty weather coming your way! Mike

  11. Stephanie Says:

    on September 12, 2014 at 3:34 am

    I have a pond that holds about 1400 gallons. I have fish in there at the moment. Have tried over the years, and they seldom all make it through the winter. I use a pond heater to keep a hole in the ice. I was thinking about adding a second one on the other side of the pond. But I was also wonder about circulating the water as well, but I am not sure what size air pump to buy. And would i need to put the hose in the middle of the pond? I was looking at a Pondmaster air pump. I bought eight Koi earlier this year and would really like to see them come spring. When my pond freezes, it typically freezes until spring. Last year lost them all even with a hole in the ice.
    Thoughts and advice?

  12. Mike Gannon Says:

    on September 23, 2014 at 11:27 pm

    Hello Stephanie, thanks for commenting! Yes you should have an air pump going during the winter months and the PondMaster air pumps are pretty good choice. Make sure you choose a model that will be strong enough to push to the bottom of your pond and try to use (2) points of aeration! -Mike

  13. Tina L McGrath Says:

    on November 18, 2014 at 2:41 am

    I have a small backyard pond – about 12 feet long x 5 feet wide by 2 1/2 feet deep. I added 5 small goldfish about 2 months ago. I wasn’t thinking ahead and did not buy a deicer. The pond is frozen and I’m not sure if the fish will live through the night if there isn’t an area of the pond that isn’t frozen. It’s too late tonight to go to a store – they are all closed. It is 12 degrees and will be all night long. What do I do if I can’t get to a store until tomorrow?

  14. Mike Gannon Says:

    on November 18, 2014 at 12:01 pm

    Hello Tina, I hope this reply is not too late. I’m going to say that it is pretty likely your fish will do ok in the short term. Unfortunately I don’t think there would be much that I could recommend doing with 12 degree weather. Once the stores are open I not only recommend a de-icer but also using an aerator during the winter months as well. I hope your fish are ok! Thanks for reading the blog and if I can help any further I am happy too. -Mike

  15. Matt Says:

    on November 29, 2014 at 11:30 pm

    I have a 1/4 acre pond with trout in it that is 9-10 ft deep at the deepest point. I have an 1/4 HP aerator in it running 24/7 and the water did not seem to be freezing over at all around it until we got a couple really colds days of weather and the whole pond froze over. The aerator is at the deepest part of the pond and I really don’t want to move it around every fall to shallow water if I don’t have to. The pump is shared between 2 – 1/4 acre pounds and the other pond has plenty of unfrozen water but the air hose length is about 1/4 the length into that pound as the one that froze over. I think I am hearing really nothing to worry about as long as the aerator is running right?

  16. Mike Gannon Says:

    on November 30, 2014 at 6:09 pm

    Hello Matt,
    Yes, as long as both diffusers in each pond have air bubbles coming up you should be ok. When one length of hose is shorter than the other length of hose the shorter hose will usually get more of the pressurized air; so be sure that the diffuser that has the longer length is still blowing bubbles!! Ideally you should be moving the diffusers to a shallower area of the pond during winter, but many people do not move them, it is not always a problem, however the “best practice” would be to move it to a shallower zone, OR keep your diffusers in an area that is not too deep and not to shallow so you don’t have to move them each season..

  17. Matt Says:

    on December 1, 2014 at 12:51 am

    OK I can’t really move the diffusers now but I adjusted the flow so there is more bubbles in the small pond (were the fish are at) and less in the swimming pond (that never froze over) in hopes the small pond will not freeze over again. If the big pond freezes over now not to worried about that because there’s no fish in it but I still want to reap the aeration benefits in it so that the muck continues to be cleaned up by bacteria there.

  18. Cathy Says:

    on March 18, 2015 at 3:49 pm

    Hi. Thank u so much for this informative blog!! I live in New York on Long Island. This past winter has been exceptionally cold. Even with a bubbler, my pond froze over a few times. My pond is about 5000 gallons. The depth is 24 inches in the center. I hired people who claimed to be experts to re- do my pond!! The last expert robbed me of $13000.00 dollars. I feel like a fool. I’ve been hoodwinked on more than one occasion in hopes that my pond could work efficiently so that I could enjoy my beautiful fish. In the ice I observed one of my koi frozen!! You could just imagine my horror!! And that was in December. Since then, the pond has been at a constant freeze. I am panicked and I pray my little guys are alive. My point here, is that, I have learned a very expensive lesson. Please be careful not to hire landscapers or concrete contractors claiming they know how to build ponds. Please do the research needed!! And if anyone knows of any good pond builders on Long Island. Please email me at Thank you

  19. Mike Johnson Says:

    on March 5, 2016 at 8:22 pm

    I made the mistake of trying to break the ice during a couple of really cold days.
    Now my pond is dropping water level 3-4″ in 24 hrs. Pond size is 6×10 ft, 32″. Has this resulted in damaging or cracking the liner.
    Thanks for response.

  20. Mike Gannon Says:

    on March 17, 2016 at 1:45 pm

    Hello Mike, thanks for reaching out. It is difficult for me to say whether the liner has been compromised, but I would guess that it was not affected by opening the ice.

  21. Paul Says:

    on July 12, 2016 at 3:30 am

    Is it possible to winter fish in. A 55gallon preformed pond? Such as the one in the website I posted from Amazon? I live in Calgary and we have somewhat cold winters but usually get plenty of Chinook winds which warm things up to around +5 celecious. This is my first pond.

  22. Mike Gannon Says:

    on July 13, 2016 at 7:21 pm

    Hi Paul, thanks for reaching out. I do think it would be a bit of a challenge keeping fish outdoors in a 55 gallon container during colder temps, and the possibility of cold snaps could be deadly in such a small volume of water. I’m not sure I’d take the risk and would maybe try to keep my fish indoors for the winter. Good luck! -Mike

  23. elizabeth Says:

    on December 16, 2016 at 3:56 pm

    i have three filters running in my pond, so three sources of running water. is this enough so that i do not need to keep a hole open. which i have done with boiling water. tired of that

  24. Mike Gannon Says:

    on December 24, 2016 at 2:13 am

    Hi Elizabeth. On the face of your question I’d say it sounds like you should not have to use boiling water; however, there are too many variables and unknown info about your pond that I am not aware of to give any solid advice on this… 🙁 Tell me more! -Mike

  25. amanda Says:

    on January 6, 2017 at 5:09 am

    The new home we just moved into came with a small decorative koi pond. It’s about 4 feet long but I’m not exactly sure how deep it is. It came with many very small koi fish all around an inch or two long (or less). The pond appears to have recently frozen over. Is this a problem? Will the small koi be able to manage? We currently have -6 C weather. Thanks in advance.

  26. Mike Gannon Says:

    on January 6, 2017 at 8:10 pm

    Hello Amanda, congratulations on your new home and new pond! Generally speaking your fish should be ok still, but I am missing alot of information. I would recommend using some sort of aeration for your pond during the winter months. You will not have to feed your fish until Spring and water temps are higher. -Mike

  27. Muriel Says:

    on January 16, 2017 at 2:04 pm

    Hi Mike. My concern for my pond is during the summer month the water level reduce due to lack of rain. With the change in the temperature for this winter, the water was warm at various time than would freeze. I notice this was first year I seen so many fish surface in this winter. Our reason change in temperature that cause the pond to freeze, I am now find fish frozen at the surface. The aeration system has been on , an you tell what cause this and what can I do now to prevent even more deaths. Thank you

  28. Mike Gannon Says:

    on January 16, 2017 at 6:32 pm

    Hello Muriel. Thanks for reaching out. I’m very sorry to hear about your fish. Unfortunately I don’t have enough information to really be able to tell you what may have happened since there are numerous variables that could have affected your livestock. I usually recommend that my customers move their aeration diffusers to shallower water in their pond during colder season. Sorry I cannot help that much… -Mike

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