Winter Pond Care in Canada: Protecting Fish, Plants and Pumps

A backyard pond can come through a Canadian winter in good shape, fish included, if you prepare it in fall and keep one thing in mind: gases need to escape through the ice. Goldfish and koi can handle cold water. The risks to watch are a sealed-over surface, too much rotting organic matter and a pond too shallow for your climate. This guide covers leaf netting, when to stop feeding, keeping a hole open in the ice, storing pumps and UV clarifiers, and what to do with pond plants. It draws on advice from the Minnesota Water Garden Society, Virginia Cooperative Extension, the Ontario government and Ontario's Electrical Safety Authority.

Early fall: net the pond and clean up

Leaves that sink to the bottom rot over winter, using up oxygen and releasing gases under the ice. Virginia Cooperative Extension's guide to winterizing water gardens recommends netting the pond each autumn to catch falling leaves and removing dead plant material promptly.

1. Stretch pond netting over the pond before the trees drop their leaves, and anchor the edges so it doesn't sag into the water.
2. Empty the net regularly. A leaf blower or yard vacuum helps clear the lawn around the pond before leaves drift in.
3. Skim out floating debris and scoop out as much sludge from the bottom as you can without disturbing the fish too much.
4. Take the net off before snow load can tear it or pull it into the pond.

Stop feeding by water temperature

Goldfish and koi are cold-blooded. As the water cools, their metabolism slows and they can't digest food well. Undigested food and extra waste foul the water. Go by a pond thermometer, not the air temperature:

• As water cools in fall, cut back the amount and switch to an easily digested cold-water or wheat-germ food.
• The Minnesota Water Garden Society, which deals with winters much like ours, advises stopping feeding when the water drops below about 10°C (50°F), and not starting again until spring warms it back above that.
• Fish that come up to the opening in the ice in winter are looking for oxygen, not food. Don't feed them.

Keep a hole in the ice, and never smash it

A frozen-over pond traps carbon dioxide and gases from decomposition, and oxygen can't get in. Keep at least a small opening all winter. The Minnesota Water Garden Society says roughly 30 cm (12 in.) across is usually enough, but it must stay open all season.

Floating de-icers

A thermostatically controlled floating de-icer switches on when the water nears freezing and keeps a patch of surface open. We carry pond de-icers alongside our pond netting and liners. A de-icer's job is to keep a hole open, not to heat the whole pond.

Aerators and bubblers

An air pump with an air stone also helps keep a hole open and adds oxygen. Place the air stone part way down, not on the bottom. In winter, fish rest in the slightly warmer water at the bottom, and strong circulation mixes cold surface water down into it. Aim for a gentle stream of bubbles, not a rolling boil. The same applies to running a water pump in winter: don't let it pull cold surface water down into the deep zone.

Never break the ice

Hitting the ice with a shovel, hammer or axe sends shock waves through the water that can stress, injure or kill dormant fish. If the pond does freeze over, set a pot of hot water on the surface to melt an opening gently, and repeat as needed until you can get a de-icer in place.

Electrical safety

De-icers, pumps and aerators put electricity close to water. Ontario's Electrical Safety Authority advises that outdoor outlets should have ground fault circuit interrupter (GFCI) protection with weatherproof covers, and that only extension cords rated for outdoor use should be used outside. Check the cord and plug before winter, keep connections off the snow, and have a licensed electrical contractor add a proper outdoor outlet if you don't have one near the pond. Rules vary by province, so check with your provincial safety authority.

Pumps, filters and UV clarifiers

Unless you plan to keep a pump running for circulation, shut down the waterfall and filter system once the water gets cold, and store the equipment where it won't freeze.

• Submersible pumps: disconnect, remove, rinse and store in a frost-free place. TotalPond's winter checklist suggests keeping a submersible pump in a bucket of water indoors so its seals and moving parts stay wet. Check your own pump's manual first, since instructions vary.
• UV clarifiers and pressurized filters: drain, clean and store indoors. Water left inside can freeze and crack housings and internal parts.
• Hoses and tubing: drain and coil them so they don't split.

Spring is a good time to replace worn impellers, bulbs and tubing. See our pond pumps and tubing and pond filters and UV clarifiers.

Pond plants and fish

Plants

Cut back hardy marginal plants and water lilies after the first frost browns them, and remove the dead leaves so they don't rot in the pond. Virginia Cooperative Extension recommends moving hardy plants such as water lilies to the bottom, in at least 50 cm (20 in.) of water. Tropical plants won't survive a Canadian winter outdoors. Bring them inside or treat them as annuals.

Is your pond deep enough?

The Minnesota Water Garden Society notes that a pond at least 90 cm (3 ft) deep is unlikely to freeze solid. Shallower ponds, and ponds in the coldest parts of the Prairies and the North, may freeze too deeply for fish to survive. In that case, overwinter fish indoors in an aerated tank.

Never release pond fish

If you're downsizing or giving up the pond, don't put goldfish or koi into a creek, lake or storm pond. The Ontario government's goldfish page identifies them as an invasive species and asks people not to release live fish into lakes, rivers or streams. Rehome them through a pet store or pond club instead.

Winter pond checklist

• Net the pond before leaves fall, empty the net often and remove it before heavy snow.
• Clean out sludge and dead plant material.
• Stop feeding once water stays below about 10°C.
• Install a de-icer or gentle aerator to keep an opening all winter. Never smash the ice.
• Plug outdoor equipment into GFCI-protected outlets using outdoor-rated cords.
• Store pumps, UV clarifiers and filters frost-free, following each manual.
• Sink hardy lilies to the deep zone and bring tropicals indoors.

Doing the rest of your fall yard work? Our guide to fall overseeding and winterizing your lawn pairs well with pond season.

Frequently asked questions

When should I stop feeding pond fish in the fall?

Stop once the water temperature stays below about 10°C (50°F). Fish can't digest food well in cold water, so don't feed again until spring warms the water back above that.

Why do I need a hole in the ice on my pond?

An opening lets carbon dioxide and gases from decomposition escape and lets oxygen in. A fully sealed surface can build up gases that harm fish.

Is it safe to break the ice on a frozen pond?

No. Hitting the ice sends shock waves through the water that can injure or kill dormant fish. Melt an opening gently with a pot of hot water, then use a de-icer or aerator.

What should I do with my pond pump over winter?

Unless you keep it running for circulation, remove it, rinse it and store it frost-free. Some makers suggest keeping submersible pumps in a bucket of water, but follow your manual.

Can I release my pond goldfish into a nearby creek?

No. Goldfish are invasive in Canadian waters, and Ontario asks people never to release live fish into lakes, rivers or streams. Rehome them through a pet store or pond club.