How to Winterize Your Fish Pond (6 Timely Tips)

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Keep your garden pond fish and plants alive with these cold weather preparation and maintenance tips. We’ve covered the basics to protect everything through the winter months.

Whether you are building an inground or above-ground pond, the basics are the same. If you are just getting started, see the complete guide to building a backyard pond.

Winter Pond & Fish Care

Goldfish wearing a red hat near a winter garden pond.

There is no reason why you can’t keep fish and plants safe and happy in a garden pond during the winter—even in a cold climate.

These tips cover the basics. Be sure to make preparations in fall for the cold months ahead.

Getting Started
Winter Pond Preparation & Care

Getting Started

Backyard garden in winter. — Two small ponds in the winter garden

If you live in a cold climate that gets winter freezes, you will need to do a few things to keep your pond, fish, and plants safe during the colder months.

I live in southwestern Ontario, Canada where winter temperatures can dip to around -20°C (-5°F) with average lows of around -10°C (14°F). My pond would freeze solid and the fish would not survive without following the tips below.

If you are in hardiness zones 4 to 8 in places like Ontario, New York, and the Midwest, you will likely have conditions similar to mine.

How deep does pond need to be for fish to survive in winter?

When I built my first pond, I kept hearing that there was no way I could keep the (cold-water) fish alive (and happy) all year-round in a cold climate in a pond that was less than 2-feet deep. Thankfully, that was not correct.

It doesn’t matter how deep the pond is, it just matters that the water is moving and not frozen.

As long as the water is circulating and there is an air hole (if ice forms) to allow oxygen in and gases out, fish and plants should be fine.

The colder it gets, the slower the fish will be. On the coldest days they will rest low down in the pond, essentially dormant until things warm up.

While you can keep a shallow pond safe all winter, the advantage to a deeper pond is the water near the bottom is less likely to freeze, even without a pump running. Plus the extra depth gives the fish a place to rest far from the hands of hungry predators like raccoons.

But, a shallow pond will work too. As said, I’m here in Canada and have taken care of several ponds that are just two-feet deep (or a bit less) and so long as I keep the water moving with a recirculating pump, the fish are fine.

What kind of fish survive winter in a pond?

The fish we’re talking about are cold-water fish such as goldfish, shubunkins, and koi. You would not keep tropical fish in a garden pond in a cold climate.

If you are in a much colder climate than I am, I’m guessing it would require quite a lot of power (energy) to keep a large pond running throughout the winter, but it does not take much in a moderate cold climate like mine.

I use both a recirculating pond pump and a floating de-icer (to prevent the surface from icing over). I’ve explained more (below).

Should I cover my pond in the winter?

No. If your pond is covered, it could prevent or impair the release of potentially hazardous gases from within the water—gases that can kill the fish. That’s also why we do not let the pond ice over. You want to ensure the water has movement (by keeping a recirculating pump running) and make sure your fish always have access to fresh air.

I know pond companies recommend a lot of additional products (chemicals, activated pond carbon, beneficial bacteria, and accessories like covers) but I have never used any of these things in my twenty years of pond care so I have no recommendations to offer.

Winter Pond Preparation & Care

Fall Tasks

As the weather cools in fall, it’s time to get your pond, fish, and aquatic plants ready for the season ahead.

1Clean Up and Lower Potted Pond Plants

Hardy plants (not tropical) and cold-water fish can survive in a cold pond so long as they don’t freeze.

Tropical aquatic plants should be removed and stored indoors.

It’s also time to remove any debris including dead and decaying plants and leaves.

2Set Up Winter Pump

A recirculating pump will keep the water moving, preventing it from freezing up. I also keep the waterfall running in my larger pond.

If you need more information on choosing a pump, my guide for starting a new pond has tips.

Submersible Pond Pump | Amazon

I sit my winter pump about two feet below the surface and attach a short length of pipe to aim the water output upwards.

I keep a floating de-icer running to ensure there is always a large airhole when the surface is icing over. You could also use an aerator like this one to keep the water moving.

Whatever you use, be sure the specific one you are choosing will function in colder temperatures.

On colder days, the fish will be dormant near the bottom of the pond. On warmer, sunny days, the fish may be more active near the surface.

3Stop Feeding Fish

Cold-water fish start to slow down and rest lower down in the pond (where it’s warmer) once water temperatures are consistently below 50°F (10°C).

They appear dormant (not moving) when temperatures drop to around 39°F (4°C) or lower.

If you feed your fish, reduce amount, or stop depending on how active the fish are. Otherwise, the feed will just rot in the pond.

Personally, I do not feed my fish at any time of year, instead letting them live off the natural fauna and flora within the pond.

Winter Tasks

4Have a Spare Pump Ready to Go

Buy a second recirculating pump so you have a backup in case your main pump stops working.

If the pond does start icing over, you won’t have much time to swap out pumps before your fish are in serious trouble.

And be sure to check on your pond at least once a day—and more often if the weather is really cold. If the pump stops, it can only take a couple of hours for a pond to freeze up.

5Use a De-Icer

You can also use a floating pond heater, also called a de-icer, to ensure you always have an air hole in the surface of pond, even if ice forms around it.

Pond de-icers are electric-powered, floating plastic disks with heat coils inside. You may see them sold as de-icers for livestock water troughs. There are various styles.

I use de-icers (pond heaters) in both of my ponds.

If you can, get one with a thermostat so it’s only warming the pond when the temperature is near freezing.

Watch out for warm spells. The added heat (and light) can encourage algae growth which starts speeding up at 16°C (60°F).

But, in the cold, winter weather, they are excellent for keeping a section of the pond water liquid and not frozen.

5Check Pond Daily

Make sure the pump is running and there is always a large air hole in case of a deep freeze.

Unhealthy gases can form under pond ice and poison the fish. Plus, the other wildlife in your garden including birds will rely on this fresh, moving water for hydration.

It’s amazing how many animals come to drink at my pond on a cold, winter day!

Spring Tasks

6Remove De-icer and Restore Plants

When the risk of freezing temperatures is over:

Raise the plants back up to their usual positions.
Clear out any stringy algae (I used a forked hoe).
Clean the pump filter (see my trick here for filtering pond water without chemicals).
Bring back tropical aquatic plants from winter storage.

The fish will take care of themselves.

Winter pond care is pretty simple. If you take care to keep the water running, your fish and hardy plants should be fine when spring returns.