The Complete Story of Our Koi Pond (13 Years in a Chicago Garden)
Every week, people stop outside our fence and ask the same question—especially in winter:
“You have fish in there?”
Yes. We do.
And after more than 13 years of keeping koi alive through Chicago winters, we’ve heard just about every question you can imagine. On a rainy afternoon, we finally sat down and answered them all—winter survival, predators, baby fish, mistakes, and everything in between.
This is the full story of our pond: what we’ve learned, what we got wrong, and what we’d do differently.
What Happens to Koi in Winter?
This is the number one question—and the answer surprises most people.
We don’t do anything.
When water temperatures drop, koi go into a semi-dormant state (not true hibernation, but close). They sink to the bottom of the pond, slow their metabolism, and stop eating entirely—often for up to five months.
Which leads to the next question we hear all the time:
“How do you feed them when the pond is frozen?”
You don’t.
What Happens to Koi in Winter?
This is the number one question—and the answer surprises most people.
We don’t do anything.
When water temperatures drop, koi go into a semi-dormant state (not true hibernation, but close). They sink to the bottom of the pond, slow their metabolism, and stop eating entirely—often for up to five months.
Which leads to the next question we hear all the time:
“How do you feed them when the pond is frozen?”
You don’t.
What Kind of Fish Do We Have?
Our pond is mostly koi, with a few goldfish (including shubunkins).
- Koi are essentially ornamental carp
- Goldfish tend to stay smaller and often stick together (ours definitely do)
And yes—most of our fish have names. Many are inspired by Star Trek, which older visitors appreciate more than the younger ones!
How Many Fish Do We Have?
The number changes over time, but typically we have around 20–22 fish.
Over 13 years, we’ve lost a few—mostly due to age or extreme winters—but overall, survival has been remarkably good given the climate.
Predators: What Threatens Koi?
Another very common question:
“Do hawks or other animals eat your fish?”
Hawks aren’t usually a problem, but great blue herons absolutely are.
We’ve lost a small number of fish over the years to herons. They’re stealthy, patient, and highly effective hunters. We’ve even had one fish fatally injured by a heron that couldn’t lift it out of the water.
Still, losses have been minimal considering how long we’ve had the pond.
Do Koi Have Babies?
Yes—and it’s not always as peaceful as you might imagine.
When water temperatures reach about 60°F:
- Females develop eggs
- Males chase and push females against rocks to release them
- The eggs are then fertilized
This process, called spawning, is:
- Very active
- Quite messy
- And surprisingly violent
We usually let the fish eat the eggs to prevent overpopulation. But if we miss a spawn, hundreds of tiny fish can hatch and hide among the rocks.
By the time we notice them, they’re often too fast to catch—so occasionally, we end up with new additions whether we planned to or not.
Do Koi Get Along?
Generally, yes.
Koi are peaceful fish and don’t fight. The exception is during spawning, when things can get aggressive—especially for females.
Do Koi Have Teeth?
This is a favorite question from kids.
Yes—but not where you think.
Koi have pharyngeal teeth located at the back of their throats. They use them to grind food, not to bite.
How Big Do Koi Get?
Our largest koi, Captain Picard, is over 18 years old and enormous—likely 30–50 pounds.
It once took three people to lift him during a pond cleanout.
Koi grow much larger than most people expect, which leads directly to one of our biggest lessons…
How Deep Is the Pond? (And Our Biggest Mistake)
Today:
- Main pond depth: 4 feet
- Secondary pond: about 3 feet
Originally? Just 2 feet.
That was a mistake.
In cold climates like Chicago, shallow ponds can freeze too deeply, putting fish at risk. Early on, we even built a greenhouse structure over the pond each winter just to keep it from freezing solid.
Eventually, we rebuilt it—deeper, larger, and far more stable.
Advice:
If you’re building a pond, make it as large and deep as you reasonably can from the start. Almost everyone ends up expanding later.
Our Biggest Disaster
One night, a decorative water feature detached and pumped thousands of gallons out of the pond.
We woke up to:
- Nearly empty pond
- Fish huddled in shallow puddles
- Water trapped beneath the liner, lifting it
It could have been catastrophic—but thankfully, everything survived.
Is a Pond a Lot of Work?
Short answer:
Yes… and no.
When everything is working properly:
- Routine maintenance is minimal
- Mostly cleaning filters and basic upkeep
When things go wrong:
- It can be a lot of work (and stress)
Do Ponds Overflow?
Not really.
Even in heavy Midwest storms, excess water simply spills into surrounding ground areas. We’ve never had fish escape due to overflow.
How Long Do Koi Live?
It depends on conditions, but commonly:
- 20–40 years is realistic
- Some reports go much higher (even legendary cases over 100 years)
In our case, several fish are nearing or past 18 years—and still going strong.
Where Do You Buy Koi?
We’ve sourced fish from:
- Garden centers
- Specialized breeders (like Kloubec Koi Farm in Iowa)
Koi are often shipped overnight in oxygen-filled bags—something that surprises almost everyone the first time they see it.
Do Koi Eat Water Lilies?
Many pond owners struggle with this—but ours don’t.
Early on, some nibbling happened, but as the fish matured (and with regular feeding), they lost interest.
Water lilies, it turns out, are:
- Hardy
- Low maintenance
- A beautiful addition to the pond
Final Thoughts
After 13 years, here’s what we know for sure:
- Koi are far more resilient than people think
- A well-built pond can thrive even in harsh winters
- Mistakes are part of the process
- And a pond becomes more than just a feature—it becomes part of your daily life
If you’re considering building one, start thoughtfully—but don’t be afraid to learn as you go.
Have a question we didn’t cover?
We genuinely love answering them—drop it in the comments and we’ll do our best to help.