How to protect ponds from freezing in NB?

Keeping your pond from freezing solid in New Brunswick requires maintaining at least one open hole in the ice — not preventing freezing entirely, which is neither practical nor necessary in our climate.

The goal isn't to stop ice from forming (NB winters make that impossible without enormous energy costs), but to keep a small area of the surface open so that toxic gases like methane and hydrogen sulfide can escape. When a pond freezes completely solid for extended periods, these gases build up and suffocate fish and beneficial bacteria. Even a hole the size of a dinner plate is enough to save your pond ecosystem.

The most reliable method for NB ponds is a floating pond de-icer (also called a pond heater). These are thermostatically controlled electric units that float on the surface and only activate when temperatures drop near freezing — typically drawing 100-300 watts. A quality unit from a pond supply or farm supply store runs $80-$200 and will last many seasons. Position it near your pump or aerator for best results. Do NOT use a regular household water heater or improvised heating — these are fire and electrocution hazards near water.

A pond aerator or air pump is equally important and works hand-in-hand with a de-icer. Running a small aerator through winter keeps water circulating, which naturally resists freezing at the surface and maintains oxygen levels for fish. Many NB pond owners run both — the aerator handles mild cold snaps, and the de-icer kicks in during the deep freezes we get in January and February, when Fredericton and inland areas regularly see -20°C and colder.

Fish Considerations

If you're overwintering fish like koi or goldfish, stop feeding them when water temperatures drop below 10°C — typically by early October in most of NB. Fish metabolism slows dramatically in cold water, and uneaten food rots and degrades water quality under the ice. Hardy goldfish can survive NB winters in ponds that are at least 60cm deep (ideally 90cm+), as the bottom layer stays just above freezing. Koi need at least 90-120cm of depth to safely overwinter here.

What NOT to Do

Never smash ice with a hammer or axe to open a hole — the shockwave can stun or kill fish. Instead, place a pot of boiling water on the ice surface to melt through gently, or let your de-icer do the work.

Practical steps for fall prep (September-October):

Remove dead plant material and trim back marginal plants before they decompose under ice. Add a cold-water beneficial bacteria treatment in October to help break down organic matter through the winter. If your pond has a waterfall or stream feature, consider shutting it down by November — running water can actually accelerate heat loss and create dangerous ice formations around the pump.

For larger or more complex water features, a landscaper or pond specialist can assess your setup and recommend the right equipment sizing for your pond volume. New Brunswick Landscaping can match you with a local pro who handles water features — free of charge through the New Brunswick Construction Network.