Winter’s Got Nothing on Your Pond
Do you worry your backyard pond might freeze solid this winter? Not sure if your koi or goldfish will make it through the snowy Michigan season?
In this post, you’ll learn what tools and steps help keep your pond safe when temperatures drop.
By the end, you’ll know how to protect your fish, preserve your equipment, and avoid waking up to a frozen disaster.
How to Keep a Pond from Freezing
Keep a pond from freezing by using a pond aerator and a floating de-icer to maintain an open hole in the ice. This allows gas exchange and prevents oxygen loss. In harsh winters, shut down pond plumbing and monitor water levels to avoid a full freeze and protect equipment.
- Use an aerator to maintain oxygen and circulate water.
- Use a pond de-icer to keep a hole open in the ice.
- In colder climates, shut down the pond and drain plumbing.
- Add water throughout winter if the pond is running.
- Remove ice gently — never strike or break ice violently.
- Avoid feeding koi during winter.
Can koi fish survive winter in an outdoor pond?
What We Recommend to Keep Ponds from Freezing
Living in Michigan means having winters with extremely cold temperatures. Keeping the pond’s surface ice-free around here is a tall order and would require a lot of energy input.
We have found that this much energy is typically difficult to call economically feasible.
The best we can do is use a pond deicer to help mitigate a complete freeze-over and oxygen depletion.
We can also do things for the hardware of our koi ponds and water gardens.
We can drain the filters to prevent ice damage.
We can also blow out the waterlines to prevent ice damage and future plumbing repairs.
Removing pumps and sinking them into the deep spot of the pond will help them escape the damage caused by the ice.
Removing baskets, nets, and check valves from skimmers can also prevent winter ice damage.
Aeration and Gas Exchange
Why Aeration Matters
When the pond surface freezes over, it traps toxic gases from decomposing debris and blocks fresh oxygen from entering the water.
Without air movement, the oxygen levels drop fast—especially under a thick layer of ice.
That’s when fish run into real trouble.
Koi, goldfish, and other pond fish slow their activity during cold weather, but they still need a steady oxygen supply to survive.
An aerator solves this by releasing fine air bubbles from the bottom or middle of the pond. These bubbles rise, stir the water gently, and create enough disruption at the surface to stop a total freeze.
It’s one of the most important tools for keeping a pond from freezing.
Where to Place the Aerator
The right placement makes all the difference.
If your pond is around 4 to 5 feet deep, don’t drop the diffuser all the way to the bottom. That deep water holds the warmest temperature during winter, and it’s where your fish naturally gather.
Instead, position the diffuser about halfway down. That way, you’re still moving water and maintaining a hole open at the surface, but you’re not disturbing the warmest zone where fish are resting.
This gives them a stable pocket of comfort while you continue to prevent a frozen pond.
Aerator vs De-icer
A lot of people think they can use a de-icer instead of an aerator, but the two aren’t interchangeable.
A de-icer floats on the surface and gently heats a small area to keep a hole open. But it doesn’t move the water or push oxygen into it.
An aerator, on the other hand, doesn’t use heat at all. It uses airflow to move water and improve oxygen levels.
You get the best results by using both together.
The aerator boosts water movement and oxygen exchange, while the de-icer prevents that movement from getting sealed under a solid sheet of ice. It’s a tag-team approach that keeps your pond healthy all winter.
Using a Pond De-icer
When to Use It
You don’t need to plug in a pond heater at the first snowflake, but once the surface starts to freeze, it’s time.
A floating de-icer or pond heater activates when temperatures drop near freezing, melting just enough ice to create a hole.
If your pond is shallow or if you’ve got a heavy snow load coming, you’ll want to get the de-icer running early, before snow starts piling up like it does around the open fields near Stony Creek Metropark.
Fish need access to oxygen all season, and you’ll avoid the panic of trying to thaw a solid frozen pond later.
How a De-icer Works
Most pond de-icers are thermostatically controlled, which means they only turn on when the water temperature gets dangerously low.
A typical 300-watt unit can melt through about an inch of ice per hour. That’s just enough to keep a small circle in the surface open, which allows harmful gases to escape and oxygen to enter.
These devices don’t warm the whole pond, and they’re not meant to. They’re designed to do one job—keep a hole open in the ice so your fish can breathe.
De-icers are easy to install, cost-effective to run, and make a big difference in fish survival.
Emergency Ice Removal
Sometimes things go wrong, and your pond freezes completely.
If that happens, the worst thing you can do is break the ice with a hammer or shovel. The vibrations can shock or even kill your fish.
A safer method is to boil water and place the hot pot directly on the ice until it melts through.
You can also use a rough-toothed saw to gently carve a hole, but take your time and avoid splashing or cracking the ice sheet.
Once you’ve got the hole open, set your de-icer in place and monitor it over the next day or two to make sure it stays open.
Should You Keep the Pond Running During Winter?
Risks of Keeping It On
In moderate climates, some pond owners keep their waterfall or circulation system running year-round.
But in places where freezing temperatures are common, it’s usually safer to shut it down.
Ice can form in your return lines or around your waterfall, blocking the flow and pushing water out of the pond. That could drop your water level overnight and leave your fish stranded in a few inches of cold water.
Frozen pipes and fittings can also crack, costing you money in spring repairs.
If you want to avoid these headaches, shutting things down is often the smarter move.
Shutdown Steps
If you’re shutting your pond down for the winter, timing and technique matter.
Most folks winterize their pond in late fall—right around the time families head out for holiday lights at Greenfield Village and overnight frosts start to stick.
Start by draining your plumbing lines and disconnecting any check valves or external filters. You don’t want water sitting in those pipes all season—it will freeze and expand, causing cracks.
Some people remove their pump completely, but if it’s safe at the bottom of the pond, you can leave it submerged. Just be sure to run it for a few minutes every few weeks to prevent the impeller from locking up.
Put disconnected parts indoors where they won’t get brittle from the cold.
Water Level and Top-Off Needs
Ice doesn’t just sit on the surface—it actually pulls water from the pond over time.
Between evaporation and ice formation, your pond’s water level can drop quite a bit during a long freeze. That’s why you need to top it off now and then during winter.
Use a hose with a slow, steady flow and add water on warmer days when the hose isn’t frozen.
Keep an eye on your waterfall or return system if it’s still running. If ice blocks the path, the water can back up or spill out of the pond entirely.
A five-minute check every week can prevent a big mess or a frozen disaster.
Caring for Fish in Winter
Fish Behavior in Cold Water
As the water temperature drops into the 40s, your pond fish start to slow down.
Their metabolism shifts into a state called torpor, where they stop eating, stop swimming, and rest in deep water near the bottom. This is a natural response to cold weather and helps them conserve energy.
But even in this slowed-down state, fish still need oxygen and stable conditions.
If your pond freezes over completely and traps gases, or if oxygen levels drop too low, the fish won’t survive.
Fish Winter Feeding Guidelines
Feeding your koi during cold weather can actually harm them.
When the water temperature dips below 50 degrees, their digestive system slows to a crawl. Food can sit in their gut and rot, leading to one of many koi fish diseases or even death.
That’s why pond owners stop feeding entirely once temperatures drop into the low 50s. Instead, focus on keeping the water quality clean and the oxygen steady.
If you want to help them prep for winter, switch to a wheat-germ food during the fall. It’s easier to digest and provides energy reserves without the risk of bloating or waste buildup during freeze season.
Species and Depth Considerations
Not every pond fish is built for winter.
Koi and goldfish can handle cold temperatures, as long as the pond has enough depth to avoid freezing solid. Most experts recommend at least 3 to 5 feet of depth for winter survival.
If your pond is shallow or lined with flat stone shelves, that shallow zone may ice over entirely. In that case, you’ll need to bring sensitive species indoors or set up a temporary tank in a garage or basement.
For deep ponds with a good hole open in the ice, most healthy fish can ride out the entire season just fine.
Cleaning and Debris Control During Winter
Winter pond care starts before the snow flies.
If your pond is full of leaves, mulch, or dead plants, that organic matter will break down under the ice. That decomposition eats up oxygen and releases toxic gases like ammonia.
To avoid this, do a deep clean in the fall.
Skim out leaves, trim back plants, and vacuum the bottom if needed. Once clean, cover the pond with a fine mesh net to catch any remaining fall debris.
In snowy areas, choose a net with holes so snow doesn’t weigh it down and collapse it into the water.
Use our pond maintenance services to prep your pond.
Aquatic Plant Winterization
Aquatic plants are a beautiful part of any pond, but they need help when the weather turns.
Hardy plants like cattails or water iris can stay in the pond if it doesn’t freeze solid, especially if they’re rooted in deeper zones.
But tropical or sensitive plants like water lilies won’t survive freezing. Trim their leaves, remove them from the pond, and overwinter them in buckets or tubs inside a garage or sunroom.
Add a little water and keep them away from direct light. This gives them a chance to bounce back strong when the temperature rises and the pond comes back to life in spring, just in time for the first weekend rush at Matthaei Botanical Gardens.
There’s S-no-w Problem with Grass Roots Pond & Garden
Grass Roots Pond & Garden makes it easy to winterize your pond and protect your fish without guessing your way through freezing temperatures. From aerators and de-icers to plumbing prep and pond shutdowns, our expert team has the tools and know-how to keep your backyard oasis safe.
If your pond freezes over every year and you’re tired of the worry, fill out our contact form today or give us a call. We’ll help you breathe easier this winter—just like your fish.
