3 Things You Should Know About Ponds In Cooler Temperatures

There are cold weather people who love big jackets and hot chocolate and there are warm weather people, who enjoy bathing suits and smoothies.  Similar to people, ponds can flourish in any season, but have special needs to succeed in the fluctuating temperatures.  During the warm weather, the main concern is algae blooms, water quality, and oxygen levels.  The three things you should know about ponds in cooler temperatures are the decline of good bacteria, vulnerability of fish, and potential runoff exposure.


1. The decline of good bacteria

Cold weather is beautiful in its own right, but there is a little less life in fall and winter compared to spring and summer.  The long days of sunlight warm the water up, helping plants bloom and fish thrive.  This is when the algae battle begins and tadpoles and other baby fish can be seen swimming around the pond. During cold weather and as the days shorten, there is less direct sunlight.  The beneficial bacteria becomes less active and lie partially dormant once the water temperature falls below 50 degrees.

Beneficial bacteria are also significantly more effective at breaking down organic material than the harmful bacteria.  Beneficial Bacteria can be added in the fall before water temperatures drop to help with the breakdown and help reduce the buildup of muck.  Good bacteria is aerobic, requiring oxygen, while harmful bacteria is anaerobic, able to survive and oxygenless environment.  Before the cold weather hits, it’s recommended to clean (vacuum) the bottom of the pond or use a Sludge Remover and complete a partial water change to help with debris build up.  Debris settles at the bottom of the pond, where the fish will need to stay as the ice builds up on the surface, and begins to decay.  As it decays, it releases harmful gases like ammonia which decrease oxygen levels.  This is what causes a winter fish kill when there is not proper aeration and an opening left in the ice for the gases to escape.


2. Fish vulnerability

Fish are cold water creatures, as the pond water cools their metabolisms and bodies slow. When water temperatures are below 50°F, they move less and no longer require food until the water warms back up again.  This increases their vulnerability to predators.  Some plants lose leaves die off and need to be trimmed back to prepare for winter, leaving the now slowed fish even more exposed.  

Daytime predators like water herons have a harder time catching the fish once the ice forms.  The fish can more easily avoid the opening in the ice.  Predators like mink and raccoons are nocturnal and are not deterred by ice.  They sneak in through the opening and prey on the lethargic fish.

Fish need hiding spots at the bottom of the pond to escape the predators.  Small plastic crates, empty pots, and PVC pipe can add a much needed area of safe haven and protection for koi and goldfish.  Adding a Pond Tint can also give an extra layer of security for fish in the colder months.  Pond netting is great for keeping pesky fall leaves out of the water, but can be used throughout winter to help keep your fish safe from predators! Aeration is always recommended year round to help keep oxygen levels high and create an opening in the ice covered surface of the pond. This gives the extra bonus of creating water disturbances near the ice opening to deter predators.  


3. Potential run-off danger

Common lawn and plant fertilizers contain nitrogen compounds and phosphorus, which help algae bloom.  Fertilizers used before the lawn turns into a winter wonderland will begin to make their way to the pond as the weather warms and the ice melts.  This creates perfect conditions for a spring algae bloom. Lawn clippings and other debris can pollute the pond and disrupt water clarity.  Try to avoid using fertilizers or pesticides in the fall as a precaution.  Lime juice and salt used to make pathways can disrupt the pH levels.

If your pond is built on a decline or in an area you worry will be subject to runoff, built a slight ridge around it, and line with rocks and other plants.  Runoff can also be an issue during rainy seasons as well, so the ridge will add protection year round.


Ponds need a little TLC to make it through the winter especially when filled with fish.  The weather cools and life slows down for everyone.  Shorts are swapped for jeans and the cooler temperatures make for ideal napping conditions.  Ponds are subject to the decline of good bacteria, fish vulnerability, and runoff during the cooler temperatures.  There are small things you can do before winter peaks to make sure you pond and its inhabitants will be ready.  


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