Snails in a koi pond?
Have you noticed snails in your pond? Some people panic when they see them, thinking they’ll take over. But most snails are totally harmless—in fact, some of them are actually helpful little fellows!
(The snail in this photo is about ¼ inch long.)
Are Snails Harmful to a Pond?
Snails Usually Don’t Hurt Anything
It’s true—the typical pond snail isn’t out to ruin your life (or your lilies). They’re mostly scavengers, eating things like decaying leaves, algae, and fish waste. Think of them as slow-moving janitors.
In Colorado, this is a fairly large snail!
Which snail do you want in the pond?
The Trapdoor Snail!
If you’re going to intentionally add snails to your pond (and many people do!), look for Japanese Trapdoor snails. These are the gold standard of pond snails.
They originated from Japan (and other parts of East Asia). Did you know the Trapdoor snail has a little “trapdoor” (hence the name) that they can close to protect themselves from predators, dryness, or cold weather? They do!
What’s so good about this snail?
They don’t reproduce like crazy, so you won’t wake up one morning to a full-blown snail invasion (not likely in Colorado anyway, but it can happen in warmer states).
They don’t eat healthy plants—they stick to the “gross stuff” like decaying matter and algae.
Here in Colorado, I’ve seen trapdoor snails grow up to about 2 inches long—which is pretty big in snail terms! They tend to stay tucked under rocks during the day and come out when things are quieter—like early morning or evening.
They move slowly, but if you watch them long enough, you’ll realize they are moving.
Ever Seen Snail Eggs?
If you’ve ever flipped over a lily pad and found a clear, jelly-like blob stuck to the underside—congrats, you’ve found snail eggs.
Most pond snails lay eggs in clusters on the underside of lily pads or floating plants. Each egg sac can have dozens of baby snails inside, just waiting to hatch and get to work.
If you see these types of eggs (and we have them in our pond), they are not from trapdoor snails! Trapdoors are livebearers, which means they give birth to teeny-tiny snails instead of laying eggs—another reason they don’t overrun a pond.
Even though the snails we have aren’t trapdoors, they’ve never been a problem. They’re often a sign of a healthy ecosystem doing its thing. If you keep fish, plants, and water quality in balance, snails will probably show up naturally.
Look at these clear gel blobs – snail eggs! Photo taken on one of our Water Lilies.
Will koi eat snails?
Yes! Well, sometimes. Koi will eat anything that fits in their mouth that is edible. So small snails (freshly hatched or under about ¼”), are fair game to them. Koi will slurp them up whole while foraging along the pond bottom.
If the snail is slightly larger than 1/4″, their shells are harder. The koi might scoop it up, but they will spit it right back out because they are too hard to crush with little koi teeth.
Japanese Trapdoor snails, once their shells are hard, are generally safe. They are too much trouble for koi to swallow.
Koi aren’t exactly dedicated snail hunters—they’ll eat them if they find them, but they’re not going to wipe out a population.
The funny thing is that snails actually swim! YES!! And whether they are tiny or large, the snail eggs are about the same size!
How Did Snails Get There in the First Place?!
Snails can arrive in your pond without any help from you. Often they’re so tiny at first you might not notice them, quietly cruising along the rocks at the bottom of the pond or hanging out on the underside of lily pads.
They can hitchhike in on plants, bird legs, or any item brought into the pond. And here’s a fun fact: snails can actually swim!
Whether large or small, their eggs are about the same size—and yes, they can float into your pond too.
A snail family!
What if I have the other kind of snail?
Don’t worry! It is rare for these snails to overpopulate in Colorado. Koi will keep the population down.
In the decade-plus that I’ve been working on and advising about ponds, I’ve seen maybe two ponds that had an overgrowth of snails. It’s rare here in Colorado ponds.
If you have hundreds of snails swarming your pond, let me know—they could potentially clog your skimmer net or pump basket. In that case, the pond would likely have other issues too. We’d need to take a look at what’s fueling the population—overfeeding fish, too much organic muck, or warm stagnant water.
But a few dozen snails here and there? Totally fine. They’re actually doing you a favor.
These snails are good too.
Introducing Snails to Your Pond
If you want to add snails rather than wait for Mother Nature to deliver them, make sure you transition them safely—just like you would with fish.
They need to acclimate slowly. The water they arrived in is likely warmer (and may have a different pH) than your pond water. Add small amounts of pond water (relative to the amount of water they are in, so maybe a handful of water) to their bag over about 15 minutes to balance temperature and pH. Let the bag float in the pond water (in the shade) for a while.
The water temperature needs to be within 5 degrees. So if the water in the bag feels the same to your hand as the pond water, it should be ok. If you feel a difference, you aren’t done balancing it.
After the pH and temperature has been balanced, release them gently into a shallow area. Don’t worry if they float at first—sometimes air gets trapped in their shells. They’ll take care of that themselves.
Kristi's Tips
Remember, snails are a part of a healthy ecosystem and while they do consume organic material, it’s not enough to be noticeable. So don’t call me up saying “I added snails but still have algae.”
When you are balancing the water temperature and pH to safely transfer snails to your pond, don’t just let the bag of snails float unattended. If it is in the sun, it will heat the water up way too much. Needs to be in the shade!
Did you know algae may grow on a snail’s shell because they move so slowly? It will!
*No snails were harmed in the making of this content.
* This blog was NOT written by AI. This was written by me. I am not a professional writer, I am a pond person. Therefore, if you see a typo, please forgive me!