Use the free Pond Winter Care Guide below, right in your browser. No sign-up, no software to install, and nothing is sent to a server.
Winter is the season that tests a pond, because cold water, ice and still air change everything fish need. Fish slow down, bacteria slow down, and a sealed ice cover can trap harmful gases while blocking oxygen. A little preparation in autumn prevents most winter losses, and this planner builds a simple plan from your pond depth and your winter low temperature.
Enter the maximum depth of your pond in metres and the lowest air temperature you expect in winter, in degrees Celsius. The tool rates the winter risk as high, medium or low, and gives guidance on ice cover, feeding and pumps. Depth is the dominant factor: deeper water stays warmer at the bottom, while shallow ponds can freeze through in a hard winter.
Depth decides whether fish can safely stay outside. Ponds deeper than one metre usually hold a stable layer of warmer water at the bottom, where fish rest through winter. Ponds between sixty centimetres and one metre can work in mild winters but need an ice-free hole and careful watching. Ponds shallower than sixty centimetres are risky in any real frost, and moving fish indoors is often the safer choice.
Ice itself is not the enemy; sealed ice is. A thin ice sheet insulates the water below, but a complete seal stops gas exchange, so carbon dioxide and other waste gases build up while oxygen falls. The goal is never a fully open pond, only a small hole kept open through the coldest weeks. An air pump bubbling gently, or a floating heater, holds that hole without chilling the whole pond the way a running waterfall can.
Never smash ice to open a hole. Hammering sends shock waves through the water that can injure or kill fish resting near the bottom. Instead, melt a hole with a pan of hot water set on the ice, or keep a heater or air stone running before the ice forms. Once a hole is open, keep it open: a hole that freezes and reopens repeatedly is still far better than a pond sealed for weeks.
Feeding must stop as water cools, because fish cannot digest food properly in cold water. Below about ten degrees, switch to an easily digested wheatgerm food in small amounts, and below about eight degrees stop feeding altogether. Uneaten food and undigested food both rot and pollute water that cold bacteria cannot clean quickly. Fish live off stored reserves through winter, and they do not starve in a few cold months.
Pumps and waterfalls need a winter decision based on your climate. In light frost, running the pump keeps water moving and oxygen up. In hard frost, a waterfall chills the water, builds ice dams, and can divert water out of the pond over an ice bank, draining the pond while you sleep. If you switch the waterfall off, keep the filter bacteria alive with a small circulation or accept a slow spring restart with careful testing.
Autumn preparation makes winter far easier. Net the pond before leaves fall, because rotting leaves consume oxygen and release ammonia all winter. Cut back dead plant growth, clean the filter, and check that the pump and air pump both run. A pond that enters winter clean, with a net and an air pump ready, needs little attention until spring, while a pond full of leaves enters winter already in trouble.
Do not disturb fish in deep winter. Fish resting on the bottom are using minimal energy, and netting, moving or even heavy footsteps on a frozen edge can stress them badly. Check the ice hole daily, top up water lost to evaporation with dechlorinated water, and watch for a sudden thaw followed by refreezing, which can trap gases. Otherwise, leave the pond alone and let the fish rest.
Spring restart deserves the same care as winter preparation. As water warms past ten degrees, restart the filter gradually, test ammonia and nitrite twice a week, and resume feeding slowly with small amounts. Fish that survived winter are weak, and a sudden heavy feed or a large water change can shock them. A patient spring, with testing and light feeding, turns a pond that survived winter into a pond that thrives in summer.
Versión en español: Cuidados de invierno para estanques – Plan según profundidad