Can Koi Fish Live in Cold Water?

Koi are easy-to-maintain fish that can survive in any environment.

If you’re wondering whether Koi fish can live in cold water, the answer is yes. They can live in cold water, but only under certain conditions.

Although Koi fish can survive in both cold and warm water, a specific temperature is required to keep them healthy, as they are cold-blooded.

Their body temperature depends on their surroundings, so it is important that the tank or pond water stays in the correct temperature range.

Koi fish are more active during warm weather. As the winter season approaches, you need to ensure that you take specific measures to keep your Koi fish comfortable and healthy.

Why Do Koi Fish Feel Sluggish in Cold Water?

If you notice your Koi fish is inactive and lying at the bottom of the fish tank, it may be because of the water temperature. The bottom of the tank is a bit warmer, so the fish may prefer that environment.

A decrease in water temperature can severely affect your Koi fish’s metabolism, causing digestive issues. Koi fish feel comfortable in water temperatures between 59-77° Fahrenheit, and any temperature above or below this range may affect their health.

What Water Temperature Do Koi Fish Prefer?

Koi fish prefer moderate-temperature water, neither too cold nor too warm. Anything below 77 degrees and above 55 degrees Fahrenheit is considered ideal for their healthy growth.

During the winter season, if the tank’s water temperature falls below 40 degrees Fahrenheit, the fish will move toward the bottom of the tank to receive warmth, and stay there until the temperature increases.

Is Cold Water Dangerous for Koi Fish?

Yes, Koi fish’s metabolism is affected by cold water, resulting in stomach issues. Once food enters their stomach, it turns into toxins—which, in severe cases, can also cause their death.

In addition, when a Koi fish’s metabolism is slow, their digestive system cannot digest food properly, thereby increasing their susceptibility to various diseases. Therefore, you must monitor their feeding limit in cold water.

Do Koi Fish Die in Freezing Water?

Koi fish can hibernate during freezing weather. However, continuous exposure to cold water for an extended period can cause their death. Koi fish can freeze in freezing water if there is no water pocket for them to breathe inside the water, which can cause suffocation.

To prevent this from happening, make sure to keep the fish tank warm through artificial means.

Why Do Koi Fish Require Warm Water?

Koi fish prefer warm water so they can easily digest their food. The fish can adapt to warmer tank temperatures and remain active unless the water temperature is too high. When the water temperature is too high, the dissolved oxygen in the water starts to deplete.

Koi fish need oxygen to digest their food; in the case of water temperature above 90 degrees Fahrenheit, they will stop eating due to the low oxygen level in the water, which in severe cases, can result in their death.

Measures to Keep Koi Fish in Cold Water

During the winter season, when the fish tank’s water temperature is cold, you must take specific measures and precautions to keep the fish healthy and active.

Here are a few essential tank maintenance measures you can take during the winter season to keep your Koi fish thriving.


Tank cleaning is an essential step for keeping your Koi fish healthy. It is advised to clean the fish’s tank weekly or bi-weekly. Remove dirt, debris, leaves, or other decaying matter from the fish tank to prevent the fish from consuming it and falling sick.

Koi fish stop eating in cold temperatures, and as a result, the food starts to rot inside the water, leading to oxygen depletion and diseases.

In severe cases, deadly diseases can spread from one Koi to another, and the whole population of Koi can be affected. To remove any waste and decaying organic matter from the tank, use a net-based skimmer with a solid handle to get rid of waste from the fish’s tank.


Install biological and physical filters to keep the tank water clean. In this process, the water is pumped from the Koi fish’s tank into the filtration tank and the filtered water is returned to the Koi fish’s tank.

However, when the temperatures are mild and above 50 degrees Fahrenheit during winter, you can install the filtration pump inside the fish’s tank for cleaning. Monitor the filtration pump assembly daily to ensure it is working correctly and not harming Koi fish.

Pond Depth

During winter, the bottom of the tank is the Koi fish’s favorite spot to stay due to its warmer temperature compared to the rest of the tank. To keep your Koi fish healthy during winter, it is essential to use deep ponds, where they can lay or swim if the temperature is favorable.

Keep the Koi fish tank/pond’s minimum depth at least 36 to 48 inches deep. A deep Koi fish pond or tank always provides better temperature consistency for Koi fish. As water can retain heat, the large volume of water in the Koi fish tank will retain heat for their survival in the winter season.


In freezing temperatures, you can keep the fish’s tank temperature warm with the help of a floating heater. After breaking the surface ice of the tank, place the heater with a fixed optimum temperature to float in the Koi fish tank or pond and monitor its temperature with a digital thermometer.


Deicer can be a helpful tool for keeping a hole open on top of an icy Koi pond. Not only does it help heat certain portions of your Koi fish tank or pond, and prevent the water from freezing, but due to the presence of water pockets, the fish can easily survive in the fish tank during the colder months.

You can replace the tank heater with a deicer as it is safer than a heater for maintaining the temperature of the fish tank or pond. Deicers don’t alter the p.H of the tank due to high temperature, which is essential to control for the fish’s growth.

Hoop House

Hoop houses are like greenhouses; they contain net cover and plant setup, which you can easily place over the Koi fish pond or tank.These hoop houses can benefit Koi fish during the winter season and add scenic beauty to your Koi fish pond/tank.

Due to the Koi fish’s sluggish nature during the colder months, they are under a lot of stress and move slowly. Thus, by using these hoop houses, you can increase the movement of your fish and prevent them from being inactive and depleted in the winter season.


Oxygen is an essential factor for the survival of Koi fish during winter. When the fish’s pond is frozen, Koi fish consume all the dissolved oxygen. Therefore, it is crucial to add oxygen to the water with the help of aeration.

You can add air stones at the bottom of your pond and, with the help of an air pump, supply oxygen below the frozen layer of pond water to keep your Koi fish active through winter. Otherwise, in case of oxygen depletion, Koi fish can die.

Feeding Cycle

It is advisable to supply good quality fish food to your Koi during the winter season. However, make sure to offer it in minimal amounts as Koi fish utilize significantly less food during winters, and excess food will only increase the pollution in the pond and affect the health of your Koi.

Koi fish are fed thrice a day for healthy growth. Still, in colder water above 55 degrees Fahrenheit, feed them once. Below this temperature, stop feeding them until the water temperature is above 55 degrees. This is because they stop eating below 55 degrees Fahrenheit and feed only turns into pollution.

Final Thoughts

Koi fish is a versatile fish that can survive in cold temperatures between 77 to 55 degrees Fahrenheit. However, they need milder temperatures to easily digest food for their perfect growth.

Hence, to keep them healthy, it is essential to take preventive and safety measures like cleaning, filtration etc., to keep them alive during the extreme cold season.

These measures are discussed in this guide so you can keep your Koi fish happy and healthy in cold water.

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