Many koi pond owners in Colorado often ask: What do koi do during the winter? Surprisingly, you don’t need to move your koi indoors from November through March, even though Colorado’s temperatures frequently dip below freezing. These resilient fish are well-equipped to adapt to cold conditions!
Remember, there are fish in local ponds and lakes in Colorado. They over winter too!
Koi in cold weather
Koi and goldfish are cold-blooded, meaning their metabolism adjusts with the water temperature. When winter arrives and water temperatures drop below 50°F, koi enter a state called torpor, similar to hibernation. In this state, they conserve energy, move very little, and breathe more slowly. This is why we don’t feed koi when the water temperature gets below 50°; they can’t digest it!
In our pond, the water temperature recently measured 34.6°F. The koi have settled at the pond’s bottom, completely still. The ice that forms on the pond’s surface acts as insulation, preventing the water below from freezing entirely, even during frigid weather.
This is a pond cover in the process of going up in Longmont.
The extra mile - Should you cover your pond for the winter?
Some koi lovers install winter pond covers. Yes! They really go the extra mile and put up a cover for maximum pond protection! These covers help maintain warmer water temperatures. The heat from the water and the warmth from the sun, keep the water temperatures above freezing even during serious cold spells.
Benefits of Pond Covers:
- Temperature Stability: A cover prevents the pond from freezing entirely, retaining heat from the water and sunlight.
- Debris Control: It keeps leaves and other debris from blowing into the pond.
- Predator Protection: Covers shield your koi from predators like raccoons or herons.
Covers are typically constructed using wood or PVC frames with clear poly tarps or fine mesh netting. Clear tarps are an excellent choice as they allow sunlight to penetrate, helping maintain a healthier environment for your koi.
While most fish overwinter without a cover, it is beneficial overall if you want to do it. It protects the fish and keeps their winter stress levels lower.
Different pond with the same type cover going up. This is a fine mesh netting for the cover found at The Pond Guy – Fine mesh netting She uses this for netting but switches to the tarp for the winter.
Here is a close up so you can see just how fine this netting is!
This is the clear poly tarp they have used. This particular tarp is on Tarps Plus. They come in different sizes and colors. I like the clear one because it will allow sunlight in. It is also very strong and has grommets to easily fasten to your structure.
A good look at the pond frame
The pond is cozy under here!
Colorado’s winter can vary greatly from days when you just need a jacket to frigid temperatures, but koi are remarkably hardy. With proper preparation and a little care, they’ll rest peacefully under the ice and be ready to thrive again in spring. Don’t worry if you are not up for installing a pond cover. The vast majority of Colorado pond owners don’t. Follow basic maintenance tips and your koi will remain safe and sound through the cold months.
For more advice on winterizing your koi pond, reach out to Sweetwater Ponds. We’re here to help keep your water features in top shape all year long!
Kristi's Tips
Essential Winter Pond Maintenance
Even though the fish will be in torpor, the pond still needs to be healthy. Do a partial water change (roughly 20%) on a warm afternoon just to keep the water free of excess nutrients. Be sure to use a water treatment that de-chlorinates the water. (If you did a cleanout in the Fall, this is not necessary).
If possible, bring up aerator disks to an upper level so they aren’t bringing the coldest air into the warmest part of the water all winter. Use a deicer to ensure a hole will be open during the coldest times of the winter. You do not have to put up a cover like what I am showing above. In fact, the majority of our clients don’t do this. But, if you are interested and if you want direct advice about a pond cover like this, let me know. Karen is the one who does this and maybe I can put you in touch with her. (If you’re really nice, cause she is really nice)Surprisingly, winter is an excellent time for pond renovations, repairs, and new installations. Many pond owners choose this time of year for upgrades so they can enjoy a refreshed water feature as soon as spring arrives.
If you’re considering any improvements or need advice about pond covers or winter maintenance, feel free to reach out.