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How does winter affect my pond? – Ponds & Lakes Q & A


Winter PondQ:  How does winter affect my pond? – Steve in Michigan

A:  A Closer Look at Water in the Winter…

We field many questions about water and the way it works during the winter.  With such a range of questions, here is a quick course on the physical properties of water and how they relate to your pond.

Here’s a review on density.  On our planet, matter that is denser will always be pulled down (gravity) more strongly than matter of lesser density.  Density is temperature dependant in that warmer matter is always less dense than cooler matter.  A good example is a hot air balloon, which lifts up because the air inside the balloon is warmer than the air outside.

A water molecule (H20 – don’t worry that’s as technical as we’ll get) contracts as it gets colder, causing it to become more dense.  As water closes in on the freezing point, we run into one of nature’s great exceptions.  At 39ºF (4ºC) water actually starts becoming less dense as it prepares to shift from a liquid to a solid at the 32ºF mark.  Why is this so important?  This means that water at the bottom of your pond will always stay about 39ºF because it is the heaviest.  We refer to this as inverse stratification, where a pond has a thermocline that separates warmer water on the bottom from cooler water on top (FYI, normal stratification occurs during the warmer months of the year when the cooler water is at the bottom and the warmer water is at the top).

Winter PondHow does this apply to your fish?  Fish actually get quite sensitive to temperatures below 39ºF.  This warmer 39ºF pocket on the bottom of the pond is where they tend to hang out during the winter.  This is why it is recommended that an aeration system be installed a couple feet up from the bottom of the pond to keep the 39ºF water in tact. Should you worry if yours isn’t? No, not really, mortality due to water temperature is extremely rare and NOT aerating is way more risky. The more severe issue is the toxic gases under the ice. Continuing to aerate will vent these gasses while also infusing oxygen into the water keep your fish happy and healthy.

8 Responses

  1. I am planning to treat my 1/4 acre pond with Whitecap to control duckweed in early April . Is it possible to plant aquatics (waterlilies, etc) after using Whitecap? If so, how long should I wait after application to introduce them?

    • Hi Betsy,

      It is possible to plant water lilies however you would want to wait at least 60-90 days after treatment before planting. Depending on dosage it may take a month or two for the whitecap to dilute enough to where it would not affect any other plants.

  2. I have an aeration system in our pond, 2 squares with 4 stones each. Approximately 9000 gallons 3 feet deep. We now have 1 of our big koi floating belly up. This happened last year also as we lost maybe 4 fish. Last week i did see them all around with no problem. It seems to be just the big fish that we have had for 4 years or more They look healthy. What do you think could be going on.

    • Hi John,

      Sorry to hear about the loss of your fish. If you aren’t noticing any other sores on the fish they could have just been weak or possibly that they were not able to find a calm area of the pond to stay in. Do you have a section of the pond that is deeper then the rest? Fish are going to go for the deepest point in the pond to get to the warmest water. If you have one of the plates in this section it may be disturbing their dormancy. If the pond is uniform in depth you may want to focus the aeration closer to one side of the pond for the winter months to allow one side of the pond to remain calmer. Aeration is very beneficial and having it definitely helps their survival but you do still want to leave an area undisturbed for them to relax in. Also did you stop feeding your fish once water temperatures starting dropping below 50 degrees? Once temperatures get colder fish are not able to digest food quickly. If the fish go dormant the food could remain in their system and decompose. I hope this may have given you a few tips to look into and helps you out for next season. Good Luck.

  3. Have large mouth bass in pond. They are doing great last year they had a lot of baby’s. Should I feed them pellet food?. There are a lot of frogs in the pond.

    • Hi Thomas,

      Gamefish usually survive on their own in a large pond by feeding on weeds or algae. If you would like to ensure larger food source for quicker growth you can stock the pond with minnows which reproduce quickly or you could feed them with pellets. Keep in mind though that once you get the fish used to being pellet fed you will have to keep up with the feedings. In any case you will want the water temperature to be above 50 degrees before you begin feedings.

    • Where do you get frogs? When I do capture them, they do not stay in the pond. I live on a lake and I’m sure they escape to the lake! My water right now is very merky (sp). But is never get completly clear. How can I clean the matter on the bottom of the pond without emptying it

      Thank You,

      • Hi Beverly,

        Frogs are going to stay where they are comfortable. If you have aquatic plants and places for frogs to hide they will probably come on their own without having to bring them to the pond. To clean the debris on the bottom of the pond you can use natural bacteria for organic material or a pond vacuum for silt and dirt. Only physical removal will rid the pond of non-organic materials.

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