To winterize a backyard pond in Zones 3 to 6, net it before leaves drop, clean out the muck by late October, stop feeding fish once the water stays below 50°F, and keep one hole open in the ice all winter with a floating thermostatic de-icer or a small air pump. Fish can survive under ice in a pond at least 18 to 24 inches deep. What kills them is trapped gas from rotting leaves when the surface seals solid for weeks. The open hole is not for warmth; it lets those gases escape.
Ponds in Zone 7 and warmer rarely freeze over for long, so most of this is about Zones 3 to 6.
Electrical safety comes first. Water and household current are a lethal combination. Plug every pond pump, de-icer, and aerator into a GFCI-protected outdoor outlet with an in-use (bubble) cover, use only cords rated for outdoor use, and never use an indoor extension cord. If you do not already have a GFCI outlet within reach of the pond, hire a licensed electrician to install one rather than running long cords across the yard. Unplug equipment before reaching into the water, read the manufacturer manual for each device, and replace any unit with a cracked housing or damaged cord. Never walk on pond ice, and keep children and pets away from the edge once ice forms.
Fall pond checklist
- Stretch netting over the pond before leaves start dropping.
- Skim and net out leaves weekly through October.
- Remove muck and dead plant material from the bottom by late October; leave a thin layer so beneficial bacteria survive.
- Cut back hardy marginal plants to a few inches above the water; sink hardy water lilies to the deepest part.
- Bring tropical water plants indoors or treat them as annuals.
- Switch fish to a cold-water wheat germ food as water drops from 60°F to 50°F, then stop feeding below 50°F.
- Decide whether to run or pull the waterfall pump (see below).
- Install a de-icer or air pump before the first hard freeze.
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Goldfish and koi slow their metabolism as the water cools. Below about 50°F they cannot digest food well, and uneaten food fouls the water. A floating pond thermometer takes the guesswork out. Feed a wheat germ formula between roughly 50°F and 60°F, then stop entirely until the water warms back above 50°F in spring. Healthy fish carry enough reserves to go all winter without food.
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A thermostatic floating de-icer, a pond thermometer, and a small air pump keep a gas-exchange hole open through freezes. We may earn a commission at no extra cost to you.
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De-icer or air pump: which one?
- Floating thermostatic de-icer: turns on only near freezing and holds a hole open. Best for Zones 3 and 4 and for ponds that freeze thick. Choose a thermostatic model so it is not running all winter.
- Small air pump with an air stone: keeps a hole open in moderate cold by moving water at the surface. Set the stone on a shelf about 12 inches below the surface, not at the bottom, so the deepest water where fish rest stays undisturbed.
- Both: in Zone 3 or very exposed ponds, many keepers run a de-icer and an air pump together.
Never smash ice to open a hole. The shock waves stress fish. If the pond freezes solid around a hole and you need to reopen it, set a pot of hot water on the ice and let it melt through.
Should the waterfall pump run all winter?
In Zones 5 and 6 many people keep a waterfall running, but ice dams can build along the stream and divert water over the liner edge, emptying the pond overnight. In Zones 3 and 4, most keepers shut the waterfall down. Pull the pump, clean it, and store it submerged in a bucket of water in a frost-free spot, since many pump seals dry out and crack if stored dry. Follow the pump maker's storage instructions over anything here.
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Netting stretched over the water before leaves fall keeps debris and herons out. We may earn a commission at no extra cost to you.
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Plants and leaves
Leaves are the biggest winter problem in small ponds. Netting stretched tight over the surface and pinned at the edges catches most of them. Empty it every week or two, and pull the netting before snow loads it. Compost the leaves you collect; our leaf composting guide shows how.
Zone notes
- Zones 3 and 4: Ice can reach 12 inches or more. Ponds shallower than 24 inches are risky for fish; consider moving them to an indoor stock tank with a filter and aerator.
- Zone 5: De-icer or air pump is standard. Waterfalls are a judgment call based on exposure.
- Zone 6: Ice usually comes and goes; an air pump is often enough.
- Zone 7 and warmer: Brief skims of ice. Keep netting and cleaning; skip the de-icer in most winters.
Bottom line
Net early, clean by late October, stop feeding fish below 50°F, and keep one hole open in the ice with a thermostatic de-icer or air pump on a GFCI outlet. Bring in a pond pro or licensed electrician for any wiring you are not certain about.