List of Plants Toxic to Pond Fish (Common Poison Species)

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Guide to Plants Toxic to Pond Fish, Koi & Goldfish 2022 (Poison Species)

Acacia trees are toxic to animals
As well as sharp points, many plants, such as the Acacia tree, will produce toxins as a defense mechanism to deter wildlife.

To protect themselves from being consumed, many plants produce toxins or secondary chemicals that may be toxic to some organisms, including pond fish. For example, acacia trees in Africa produce a compound called tannin, which is moderately toxic to organisms, including giraffes (the main browser of acacia trees, due to their long necks). In fact, upon being munched on, the leaves of acacia trees will emit warning pheromones (ethylene gas, specifically) to any trees downwind, alerting them to start producing tannins as well.

Many other plants, including those possibly around your pond, have similar defense mechanisms in place.

Deadly nightshade is toxic to people, wildlife, and fish
Some plants simply have poisonous leaves, berries, or root systems. Others, like Deadly Nightshade, are almost entirely toxic.

Some may only have poisonous leaves, others may only possess toxic compounds in the roots, and others may be entirely toxic, leaves, shoots, roots, berries and all (nightshade, for example). Many are only toxic to certain organisms, like humans or dogs, and others are only toxic to fish (called ichthyotoxic) or insects, others may only impact other plants to reduce competition, and still others are poisonous to just about everything. You certainly don’t want these sorts of plants in or near your koi, goldfish, or fish pond, as they could cause your fish to become ill, act oddly, disrupt metabolism, or even cause death in some extreme cases.

Here we will list a variety of plant species, both terrestrial and aquatic, that are toxic to fish to aid you in deciding which plants to avoid planting around ponds.

List of Common Plants That Are Toxic & Can Poison Pond Fish (Updated)

This list is by no means exhaustive, but rather covers some of the more common plants (with a few less common ones mixed in) that are often either naturally occurring or sought after for garden ponds. You should certainly conduct further research before incorporating any plant in or around your pond to ensure it’s safe for fish.

Common Toxic Aquatic Plant Species

Blue-green Algae

Blue-green algae cyanobacteria in a pond

While not actually a plant, it’s important to mention blue-green algae, also known as cyanobacteria, as it’s potentially quite harmful. As the names imply, blue-green algae is bluish green in color (cyan) and composed of bacteria, not algae, though it does closely resemble algae when it blooms out of control. Cyanobacteria contain a host of harmful toxins, and different species have different dangers. While the presence of some cyanobacteria is natural and even beneficial (as covered in our article on the different types of algae), if a cyanobacteria bloom occurs it can cause muscle degeneration, oxygen depletion (and asphyxiation as a result), damage the internal organs such as the liver and kidneys in addition to damaging the gills, and ultimately can result in mass fish kills.

However, the smaller the water body is, the easier it is to monitor and control blue-green algae. Simply conduct water quality tests on a daily basis to monitor nutrient levels, pH, dissolved oxygen levels, and so on. If your pond has low dissolved oxygen and high levels of nutrients such as nitrogen, you’re at risk for a cyanobacteria bloom. Simply return the water to normal, healthy parameters and the bacteria will be kept in check.

Common Toxic Tree Species

Though naturally occurring around much of the world, oak species contain compounds known as tannins that, while they likely won’t cause death, they can cause digestive upset and reduced digestive rate. Specifically, the leaves and acorns of oaks contain tannins, and can make your fish sick if they fall into the pond where they are able to be consumed. As well as this, the acorns and leaves are prone to build-up and will cause issues with water condition if large quantities are left to decompose on the pond floor.

With their ability to either be pruned into a shapely shrub (say, one that looks like an animal or statue, for instance) or trained into a mature tree with large swooping branches and fragrant needles, some pond owners enjoy having yews leaning over their water.

However, the needles and seeds are both poisonous to fish due to taxine alkaloids, though interestingly enough the berries themselves are edible (so long as the seeds are not consumed). The Japanese yew (Taxus cuspidata) is particularly dangerous, as it’s also an invasive species in Europe and North America.

Cherry (Rosaceae Prunus – all species)

All parts of cherry trees are toxic to fish

Though cherry trees are certainly beautiful with their fragrant and vibrant blooms and bright fruit, be they wild black cherry, pin cherry, choke cherry, or modern cultivated cherry, all parts of them are considered toxic to fish. They belong to the rose family and are highly sought after by gardeners and enthusiasts alike for their appearance, scent, and edible (to humans!) fruit.

However, all parts of cherry plants are toxic to fish, and the seeds (or pits) in particular contain hydrocyanic acid, also known as prussic acid. In larger animals, such as humans or livestock, these pits would have to be consumed in great quantities to have much effect. In fish, however, consuming just one or two pits could cause death. Hydrocyanic acid blocks the ability of tissues to use oxygen and ultimately results in suffocation, spasms, and death shortly after.

Similar to cherries, peach pits also contain hydrocyanic acid. In fact, anything in the genus Prunus (also known as drupes or the stone fruits, named after their hard pits), should be avoided near your pond. This includes apricots, plums, nectarines, mangoes, and so on.

All parts of peach trees are toxic to fish to varying degrees, though only the pits and the seed inside of them may cause death if nibbled on. The leaves, buds, etcetera have only been known to cause little to no effect.

All portions of black walnut are toxic, except for the meaty walnuts themselves. The leaves, roots, bark, and walnut husks (also known as modified bracts) that surround the nut and its shell all contain something called juglone toxin, which incites cellular death in plants (making walnuts exceptional at killing off competing plants around them), insects, and small organisms like fish if the plant matter is consumed. The toxin is also leached into the soil via the root system, so if you’d like to have a walnut, plant it far away from your pond. Contrastingly, if you have an existing walnut tree and are looking to have a pond, place the pond far enough away from the walnut that it won’t pose a threat (there’s not much sense in cutting down a tree if you don’t have to that does have positive wildlife value and can provide you with food – the walnuts themselves are not toxic!).

Common Toxic Shrub Species

Jasmine (Oleaceae jasminum)

Jasmine berries and flowers are toxic to fishTypically occurring as flowering vines or shrubs, some jasmine varieties can also be evergreen. With their exotic, extremely sweet fragrance and attractive five-merous white flowers, placing jasmine by your pond can be tempting. However, the berries (and some argue the flowers as well) are dangerous to most wildlife and fish, causing disruption of the nervous system due to the presence of glycoside and hepatoxins.

Nightshade (Solanaceae solanum)

Most nightshades are toxic to fish, people, wildlife

As might be expected from its name, all parts of nightshade are fatally toxic. Nightshade species are in the family Solanaceae, and in fact all members of this family should be avoided. They often have pretty and fragrant flowers and tasty-looking berries, but don’t be fooled – most types of nightshades are still considered dangerous to humans, livestock and fish alike.

In particular, the infamous Atropa belladonna, or “deadly nightshade” (pictured), which is in the same family as potatoes, tomatoes, and eggplants, has berries which are extremely toxic to organisms if ingested.

Alocasia (Araceae Alocasia)

Alocasia plant toxic to fish

Alocasia are very large-leaved tropical to subtropical plants, also known as the jewel plant for the beautiful patterning on their leaves. They’re often used by gardeners and ponders alike, as they effortlessly provide a tropical feel and don’t require much care so long as your temperatures average above 60°F year round and they can get plenty of moisture either from the soil, rainfall, or supplemental watering.

Their beautiful appearance aside, alocasia stems and leaves are toxic because they contain indigestible crystals of calcium oxalate, like taro mentioned below.

Taro, also known as elephant ear, is a subtropical to tropical flowering plant with impressive leaves that can be larger than a person! You may be a bit surprised to find this plant on this list, as it’s sold by many pond plant sellers and has been incorporated into many pond scenes as they add a tropical, exotic vibe. However, all parts of the plant are toxic to fish (as well as humans, dogs, cats, and likely many other organisms) if ingested due to the presence of insoluble calcium oxalate acid. Some pond owners may argue this, as they’ve had the plant without issue. Regardless, we recommend staying on the safe side and not having this plant in close proximity with your pond, but at least far enough away that there’s no danger of leaves falling into the water and your fish nibbling on them.

Wisteria (Leguminosaea Wisteria)

wisteria flowers toxic to fish and wildlife

Wisteria is a beautiful, vigorous woody vine that can become a shrub or even trained to be a gorgeous viney tree. With dramatic, elegant drooping clusters of flowers that range from blue to purple to white to pink, wisteria can be quite tempting to add next to your pond as it provides a very magical feel. However, the flowers are known to be toxic to most animals, and so if it’s planted too close the flowers could either fall in or be blown in by wind if the plant is further away. The seeds are also toxic and can result in illness or death. Belonging to the legume family, most others in this family should also be avoided.

Common Toxic Flower Species

Bird of Paradise (Strelitziaceae Strelitzia reginae)

bird of paradise flower contain tannins that cause digestive upset

Though an extremely beautiful and unique plant, the leaves of the bird of paradise (native to South Africa) contain tannins. These aren’t deadly, but can cause illness and discomfort if they’re allowed to build up. The seeds, however, contain hydrocyanic acid, and like cherry will result in suffocation and ultimately death if ingested. Try your best to keep these plants far from your pond, or even avoid them altogether if possible.

A relatively common flower, as it’s both pretty and easy to grow (it’s able to grow in nature just fine on its own), tiger lilies should also be avoided. All parts of it contain Lycorine alkaloids, which don’t typically result in death unless ingested in large quantities, but most often cause nausea, convulsions, and inability to properly synthesize proteins in the body until the toxin has been diluted and exited the body. These symptoms have been reported in cats, dogs, and horses that have ingested Lycorine alkaloids via tiger lilies, daffodil bulbs, or other plants containing the alkaloids, and are likely to have similar effects on fish.

Morning Glory (Convolvulus/Ipomoea)

plants that are toxic to fish morning glory

With deep green, creeping vines that sport lively blooms that open up each morning, morning glories are often planted on trellises or near things that they can climb around. Because of this as well as their white, blue, purple, magenta (or any mixture thereof) flowers, they make quite a pretty addition to water scenes. The seeds of morning glories (and of most things in the Convolvulaceae family), however, contain a chemical quite similar to LSD, called “natural LSD”, that is harmful to just about anything that ingests it. If any part of the plant is consumed, you may notice your fish acting oddly (because the effects are similar to that of LSD), refusing to eat, and producing excess waste.

An exceptionally pretty plant that grows several feet tall with showy, bell-shaped brightly colored flowers of all shades that are also uniquely patterned on the inside, foxgloves can be hard to resist, for they make a gorgeous addition wherever they are. With that being said, all parts of the plant are considered toxic to humans, dogs, deer, and fish alike (along with many other organisms) if the plant is in any way ingested. Consumption results in the heart rate slowing down dramatically or becoming irregular, and if too much is eaten then the heart can stop altogether. In fact, the cardiac and steroid glycosides present in foxglove act similar to medications used to treat tachycardia. You can plant it if you wish, but try your best to keep it away from your fish and any other pets!


107 thoughts on “List of Plants Toxic to Pond Fish (Common Poison Species)”

  1. I have a couple of floating planters in my fish pond. I would like something flowering but low growing. Are purslane, Vincas or Calibrachoas poisonous to goldfish?

    • Hi Chris,

      It’s difficult to say for many plants as there are very little studies available on their individual effects on fish, but it appears that the families of Apocynaceae (containing Vincas) and Solanaceae (containing Calibrachoas) contain some species that have shown possible piscicidal (poisonous to fish) properties –

      Again, this is just a single study representing just a few genera within the families, so it may not apply to your chosen species. However, I do know that these plants contain alkaloid compounds (most plants do; just to different degrees), which can indeed be toxic to fish, but they do need to be in high concentrations to cause serious harm. If your pond is fairly large and well maintained (i.e., good water quality), just a few floating planters are unlikely to cause major issues, especially if you make sure to clean away dropped foliage before it can leech into the pond water.

    • Hi Jim,

      Sadly, there is very little information on this pathogen and its toxicity to wildlife, so I can’t really advise here. Omitting any direct toxicity, at the very least, any apples (and by contrast, fungus), that land in the pond will certainly decay and have the potential to cause water quality issues if they’re in large enough numbers.

      • Hi Sarah,

        Paperwhites belong to the Narcissus genus, more commonly referred to as daffodils. All members of Narcissus, as far as I’ve found, are known to be toxic to animals. In particular, the bulbs and flowers contain lycorine and galanthamine, both of which are quite toxic and can cause gastrointestinal pain, loss of appetite, lethargy, loss of the ability to thermoregulate which in turn can lead to hypothermia, and even death if too much of the plant is consumed. Primary studies of toxicity have focused on dogs, cats, and horses but I’d urge that any plants in this genus be kept far enough away from ponds that there’s no chance your fish could come into contact with them or any parts of the plant could find their way into the pond.

        If you’d like to take a look at the information I found, here’s a link to one of the studies that I read through!

  2. I have Camellia’s close to my pond and a lot of their flower petals end up in my pond. Might these be toxic?
    I also have a large Photinia shrub next to my pond that drops a lot of leaves, especially the red ones, and ultimately blossom into my pond. Are these known to be toxic?

    • Hi Bernie,

      As mentioned in another comment above, almost all plants contain, to various degrees, compounds that can be potentially harmful to fish. In most cases, so long as you can remove the dropped foliage to prevent it leeching into the water, you shouldn’t have too many issues. However, we can still try to make a distinction on just how potent these compounds may be in different species and if the species has any unique properties that make it stand out.

      In terms of Camellias, it appears that some within the family (namely, “Camellia sinensis” – the tea plant!), have been identified as poisonousness to fish –

    • Are these plants only toxic if it’s consumed. Because I have an elevated big filter and was looking to plant some plants. Would the fish be fine if just the water is filtered through their roots?

      • Hi Emma,

        Yes, these plants are only toxic if consumed. You can place them in aquatic planting baskets if you want to help prevent fish from nibbling on the roots or stems, and of course be sure to clean out any dead or floating foliage daily!

          • Hi Michelle,

            All species of begonias are known to be toxic to humans and pets, including fish, unfortunately. In terms of succulents, there are thousands of species so that’s a bit tricky to answer. Do you have any particular species/varieties in mind? Ones that I know are for sure toxic include crown of thorns (Euphorbia milii), which contains natural latex that is a skin irritant and potentially toxic if ingested; kalanchoes, which contain bufadienolides cardiac glycosides that can cause heart issues if ingested; the jade plant is toxic to people and pets; and sting of pearls can cause skin irritation. I wouldn’t be incredibly concerned with the succulents as I’m assuming they’ll be planted a ways away from your pond as they prefer dry conditions, but it’s certainly better to be safe! A quick online search of whichever succulent species you’re interested in should tell you whether or not they’re toxic. Otherwise, feel free to reach out here again with the species and I’ll see what I can find 🙂

  3. Have an aquaponic system that is infected with roorknot nematodes. Seems sesame oil can kill the RKN’S, but cannot find much information about sesame’s toxicity to fish, specifically tilapia. Wondering if you know anything about the subject.

    • Hi B.H,

      Unfortunately, I don’t have any personal experience using sesame oil when it comes to fish, nor did my research on the topic turn up any information that might be helpful. Sorry about that!

      If you happen to discover anything in future, whether that be through research or your own experimentation, I’d be very interested to hear the results.

  4. Hi

    We have recently had all our pond fish die and I am wondering if it might be due to hemlock, which has invaded the banks and island.

    Any thoughts?


    • Hi June,

      What type of fish do you have, and how big is the pond? Also, have you performed any water quality tests recently? Although the hemlock could be a problem, it may not be due to direct toxicity, but more so a build-up of dead vegetation contributing to waste substances, such as ammonia. If pH readings are high (or fluctuating), and the weather is also hot where you are, ammonia can become particularly toxic to fish and other organisms and cause major issues within a short space of time.

      • Walnut will kill fish….walnuts were used in rivers to catch fish for food years and years ago. My fish died and I found part of a walnut in our estimated 2,000 gallon pond. A squirrel must have brought it there and dropped it. I was talking about what could have killed all my otherwise healthy koi. (4) I mentioned the walnut and my friend at work told me walnuts will kill fish. It is true.

  5. I would like to decorate my tank with privet plants but I don’t know if they are toxic to my tinfoil barbs and ruby sharks I’m not intending to put them there as food but to give my tank a more natural look but inevitable the fish will gnaw at them. Privet plants are beautiful garden plants but would also add beauty to my tank. What can I do please?

    • Hi Marian,

      I think the safety of this would depend on how often you could remove dropped fruit and foliage from the pond before it has a chance to decompose and cause issues with water quality. I think having grapevines certainly sounds pretty, but it would also require a lot of work and on-going maintenance, so you would probably need to take that into account before making a decision. Dropped foliage is also usually less dangerous (and easier to remove) compared to most fruits which can sink, and you definitely do not want a large amount of grapes decaying in your pond as that would lead to all sorts of problems!

  6. I have an almond tree dropping fruit and leaves in my pond I have had 3 fish die so far. My pond is greenish yellow right now and I’m afraid more fish will die. I have some over 2 feet long. Help

  7. Hi there. I have a suitable spot for a pond in Dorset, UK, that would be partly beneath the branches of a eucalyptus tree. Would fallen leaves from the tree create oil that would poison the pond? I would of course fish them out when they fall or use a net in leaf-dropping season. And there would be no fish in the pond, just wildlife.

    • Hi Chris,

      I believe that some (if not all) species of eucalyptus are considered toxic due to the high levels of polyphenols in the leaves, but whether this has the potential to harm wildlife or not will probably depend on the concentration of substance in the water and the amount of ‘leeching time’ the leaves have before you’re able to clean them out. If you’re able to clean the leaves out regularly, or if very little leaves fall in the pond, you may not have any issues. However, I’d probably advise against this if there was significant leaf fall or if you intended to have sensitive fish in future.

  8. Coincidence? I had a blue phantom pleco die after goong on a binge of eating water wisteria leaves. Is water wisteria toxic? Thanks

    • Hi John,

      That’s unfortunate to hear, but I don’t think water wisteria shares the same toxic properties as it’s terrestrial-named counterpart, and I couldn’t find anything from my research to indicate it has any toxicity worthy of note.

      Was your pleco displaying any other symptoms or behaving oddly prior to this?

  9. We had a bumper crop of apricots this year and some dropped off and rolled into the pond. I got them out when I could but the lilies are really thick hiding them. We had one 18″ koi die and he looked fine when I took him out. Now I have another about 22″ that I’ve noticed getting thin and she is usually very plump. It appears as if she is starting to bend horizontally. We have one white comet that we thought was dead back in April it is bent and looks like a dead fish floating when he is relaxing on top of the water. However he does get up some speed and eats before he disappears under the pond lily leaves again. I don’t know if the apricots are hurting them or there is something else. I don’t expect to see the one koi alive much longer. I have 7 more large koi and about 20 other goldfish born in the pond over the years. The pond is about 2000 gallons the pumps through two 55 gal filter drums into a smaller pond then overflows down a stream bed into the larger pond with the fish. We’ve had most of the large koi since we built it in 2006 since they were tiny and it pains me to see them get sick and die now. When we were working on the filters and replacing the filter box the hoses were going directly into the top pond and twice the raccoons chewed on the hoses and dragged them out of the pond causing the lower pond to be almost completely empty so there has been two complete water changes about 6 weeks ago. Any ideas?

  10. hi can any one tell me will ground ivy growing into my pond harm the fish or water there is a lot all down a 30ft side i have left it as the fish like laying in it and frogs ect sit on it and use it to get in and out thanks

    • Hi Mark,

      Apologies for the late reply!

      Whether or not it’s harmful to your fish depends – ground ivy can either be referring to creeping charlie or English ivy. If it’s creeping charlie, you’re good to go and it shouldn’t harm your fish or any other pond residents. If it’s English ivy, not only are the leaves and berries toxic, but if you live in the United States it’s a VERY invasive plant and should be removed immediately. I’m guessing that since you mentioned there is quite a lot of it, that it’s English ivy as this plant is very pervasive and overtakes areas quickly and easily.

  11. I have a Datura tree growing near my pond and some leaves fall in the pond and my after a while my fish die
    Would this be the problem?

    • Hi CJ,

      That depends on the species of fruit tree! For example, anything in the stonefruit family (such as plums, apricots, peaches, cherries, and really any other fruit with a pit in the middle) are toxic to fish, including the blooms, while magnolia flowers are non-toxic to fish. As far as I know, no ferns are toxic to fish. Further research didn’t turn up any results either. However, if you could tell me the approximate species of the fern, I could conduct more focused research and get back to you with a better answer!

  12. We have a small Rowan tree that is dropping leaves and berries into our spare small pond. We have temporarily moved all our fish into it while having a major clean and refurb on our big pond. Will they be ok with those leaves and berries. Also this smaller pond has a small waterfall will this be ok ?

    • Hi Raelene,

      Magnolia trees are not known to be toxic to fish. However, any organic debris in a pond can cause issues as it’ll add to the nutrient load and deplete dissolved oxygen levels. If your koi happen to nibble on the leaves or flower petals, they should be just fine but of course clean out the debris as soon as you can.

  13. I’ve researched a bit to see if there is any evidence that nasturtiums are toxic to koi. I don’t see any mention that any part of nasturtiums would be a problem. I want to plant them on a hydroponic wall that feeds the pond waste water over the roots and then back into the koi pond. The flowers and seeds would certainly drop into the pond and the leaves would likely trail into it. Is there likely to be a toxicity problem?

    • Hi Cynthia,

      Thanks for reading and commenting!

      You’re correct – nasturtiums are not toxic to koi, or any fish as far as my research or experience with watercress have found. In fact, many fish, including koi, enjoy eating watercress from time to time. I would only recommend cleaning out any dropped petals and seeds from the pond to maintain water quality. Your idea to plant them as part of a hydroponic wall sounds like a wonderful way to naturally purify the water while adding some excellent aesthetic – have at it, and let us know how it works for you!

  14. Are Ligustrum berries poisonous to koi? We just lost several. We had just cleaned leaves and berries from the bottom of the 100 gal. tank. There weren’t that many because it was screened but the wind could blow berries and leaves into it when it stormed which it recently. A couple later floated to the top. We were also missing a couple. We were afraid that animals had gotten them and just harmed the others. The water which had been previously clear was cloudy. We cleaned the filter but it almost immediately became dirty again. We have raccoons, possums around and although it seems to be rather late in the season, snakes. So we moved the koi, who were still rather small temporarily, and cleaned it completely and changed the water, etc. We then returned them to the pond. Later we found some struggling and belly up. We moved them indoors to our large tank. We nursed them back to health. So we thought maybe we should move the others inside. They seemed healthy. The next morning they died. They didn’t float as expected. They were at the bottom of the tank, not bloated or any marks on them. The original ones we brought in survived. The other fish in the tank were fine. So can you figure out what’s up? Sorry this is so long but it’s quite a mystery!

    • Hi Elizabeth,

      I’m so sorry that you’re dealing with this! Very unfortunate.

      To answer your question, yes ligustrum berries as well as the leaves and roots are toxic to fish (and cats, horses, humans, and dogs). They contain terpenoid glycosides, which, if an overdose occurs, disrupts digestion, heart function, and kidney function. This could be why your fish are dying. Could you by any chance provide your water quality parameters? It could be that the storm also stirred some things up in the pond and disrupted the water quality, which may have also had an effect on your fish.

      If you would like further info, here’s a very in depth list of plants that are toxic to fish:

      Here is an analysis of the effects of ingesting too many terpenoid glycosides (also known as cardiac glycosides). It explores toxicity in people, but the same effects can be observed in fish, cats, etc.

    • Hi Anthony,

      While live acacia trees secrete toxic compounds to protect themselves, I’m not sure on whether wood from a dead/cut acacia would still leach these compounds into your tank. Even treated, I would be hesitant. I don’t have an answer with certainty, but I would err on the side of caution and use a different wood – maples and beeches, for example, are low in tannins and won’t rot easily, and are not toxic to fish.

  15. Hi I would love to put a Passion flower ( climber ) to climb around my koi pond . Would this kill my fish if eaten it’s a Passiflora caerulea . Thank you

    • Hi Christine,

      Unfortunately, all parts of Passiflora caerulea are considered toxic. The exact severity of it seems to be contested and I can’t find a solid, reputable source for the information, so I’m afraid that I can’t say with certainty whether your koi would be harmed or not. I don’t wish to say one way or the other on whether it’ll kill your fish when I’m not sure, but at the very least the plant is mildly toxic.

  16. I am grasping at straws-We have a spring fed pond approximately 1acre around and 8 feet deep at the center-we have had koi for over 30 years-we are retired and winter in Florida-we returned to Massachusetts early this year due to Covid19- we usually don’t see fish until it warms mid-April so their absence didn’t seem unusual-figured they were still hibernating–but this this year all but 2 fish have disappeared -We have photos of at least 30 fish swimming on October 15, 2019-we currently have dozens of sun fish and turtles. Two weeks ago we finally saw a large koi-about 18 inches and one smaller one -about 6-8 inches-most of our koi were in the 15-18 inch range-we have no idea what could have happened-could the whole pond been contaminated ? The 2 remaining fish are very skittish. Even when we toss in food they stay well below the surface. The pond is on our 4 acres property and not easily accessible to others-Longtime neighbors haven’t seen anything unusual-any thoughts on if this could be a fish kill due to a natural poison? Is there a koi virus? Strange we have sun fish and 2 koi left. Any info would be welcome

  17. I would love to know if Bee Balm, Monarda would be safe to grow, allowing roots dipping into the pond.

    Also many pond places offer canna lilies, am I to assume they are safe enough for the fish?

    Thank you SO much for this list!

  18. Hi there,

    Terrific article. Thank you.

    I’m constructing an aquaponic system with vertical greenwal that will serve as a home for both my goldfish as well as a number of my houseplants.

    I had planned on incorporating my Alocasia Polly in amongst the soon-to-be vertical jungle, but after reading your warning about the toxicity of alocasias, I’m wondering if water running through its roots–and then back into the tank–will harm my fish.

    Thank you in advance for any advice/feedback.

    • Hi AE,

      Thank you for reading; we’re glad that you enjoyed the article!

      I would advise against using alocasia even on a plant wall that’s not directly in the tank – the water could potentially dislodge the toxic calcium oxalate crystals present in the leaves and stems. The calcium oxalate cannot be digested if ingested, and is also insoluble so the water won’t break it down.

  19. I’ve looked everywhere but I can’t find information on Mimosa trees in aquariums. Last year we cut and removed a few trees of our property and I still have a lot of long straight limbs I’ve considered using in my 55 gallon. I know how to prepare wood for tanks but I don’t want to go through it all with the mimosa just to have it kill my fish. A lot of seed pods and leaves are blown into our pond but that does not seem to be affecting the goldfish we have there.

    • Hi Ryoko,

      Thanks for reading!

      Mimosa tree seeds and seed pods are incredibly toxic to animals. The stems/branches should be fine, as the toxic alkaloids are not present anywhere except in the seeds/seed pods, but the seeds and seed pods do, like you said, blow about easily. It’s good that your goldfish seem fine, but if any fish try to eat them it would likely make them quite ill or, possibly, kill them. Anyway, I hope that this helps!

  20. I would appreciate your help if possible ,my question is Would the plant Common Nardoo be harmful to the fish in my small outdoor pond ? Thanking you in anticipation.

    • Hi Arthur,

      Thanks for reading and commenting! Common nardoo (Marsilea drummondii) is a member of the Marsilea genus, of which some species (including common nardoo) produce fruits that contain thiaminase. While small amounts aren’t harmful, thiaminase is an anti-nutrient, which means it blocks the absorption of nutrients (specifically thiamine, in thiaminase’s case) and thus can result in things like loss of appetite, weight loss, fatigue, intestinal upset, and muscle loss. If you really want to have common nardoo in your pond, you could offset this risk by feeding your fish a feed that has thiamine (vitamin B1) in it.

      With that being said, though, there is a very similar species to common nardoo that is not known to be toxic as the thiaminase present is in a lower dose than is present in common nardoo – it even belongs to the same genus, so they’re quite closely related and will function very similarly in your pond. Marsilea quadrifolia, or European water clover, can be planted in place of common nardoo and is known to be well-tolerated by fish without any known adverse effects on them. It also looks much the same as common nardoo! You may also consider Marsilea vestita, or hairy water clover, which is native to the US. We always advise using plants that are native to your area whenever possible.

      We have an article that talks about both European and hairy water clover in greater detail here, if you’re interested:

  21. Hi, I have been getting two old ceramic baths ready for goldfish. They are each in the middle of a paddock with bamboo about 10 meters away. Both baths were filled with rain water for years and have now been cleaned out and filled with tank water. They have been sitting for weeks but have gone a slightly whitish murky colour. One has a pinkish algae on the bottom. A very few bamboo leaves have fallen in, could this be responsible for the murkiness? I don’t want to put fish in as they may die. Any ideas on what might be wrong? Thanks, Julia.

    • Hi Julia,

      Do you have any sort of filtration system in the baths, either a mechanical filter and/or plants? Without this, water sitting for weeks is bound to develop issues and definitely should not have fish added until there is proper filtration and aeration in place. Stagnant water doesn’t have much, if any, dissolved oxygen and is an easy breeding ground for bacteria, algae, and the like. We recommend cleaning out the baths again, adding clean water, and getting some filtration and water movement in place plus performing weekly 25% water changes to help keep things healthy and fresh.

  22. Hello. Having just moved to a new home with an established koi pond we are in the process of removing a huge amount of ivy that has gotten out of control adjacent to the pond. We’re using nets to try and stop foliage getting into the pond so hopefully avoid problems there. There will hopefully be a decent looking fence installed in place of the ivy and unsightly garage wall beneath just a couple of feet away from the pond. The neighbours’ garage is due to be demolished and concrete base broken up.
    So I have two concerns if you could kindly advise please:. Whilst the demolishing works are going on Should I remove the koi and put them into a temporary holding tank farther away, as I expect there will be ground drilling and noise disturbance? If so how long can they be in a holding tank?
    The other is the kind of plants that may climb or be placed within the two feet gap between the pond and soon to be new adjacent fence? I have olive trees in pots, acers and currently there is a large twisted hazel overhanging the pond. I have already eliminated my initial plan of putting jasmine there to grow up the trellis but I’d like to find something suitable with flowers for a trellis against the fence and was considering a rose? Or do you have any suggestions if these are unsafe for the koi. Thanks

  23. I have a 3m by 2m pond in the garden and am thinking of planting a Mango tree near it, partly to create some shade for the pond. In the pond there are a number of Koi and common goldfish. Are the leaves of Keitt Mangos toxic?



    • Hi Whitney,

      That’s very cool that you propagate your plants using your fish tanks! I don’t have specific personal knowledge related to black pepper vine (I’m assuming you’re talking about the species Piper nigrum as that can form vines?), but I did some digging and found a study that explored its primary component, which is peperine, and its effects on humans, waterfowl, and overall water health. The study found no adverse impacts to any of those, and the fact the plant contains peperine and capsaicin (found in spicy peppers), that should deter any fish from wanting to try eating it, anyway. In fact, peperine is often extracted from black pepper to be used as a natural animal repellent to deter them from getting into homes or gardens. From this information, I would conclude that black pepper vine is not toxic to fish, and they will also likely stay away from it. Before putting the cuttings in the tank, though, I would give them a day or two to sort of “scab over” to help reduce any of these compounds leaching into the water.

      If you’d like to see a pretty detailed report on peperine toxicity, I found this:

  24. Hi, I’m looking to plant up a small rockery behind my pond, maybe a few alpine plants or low growing ground cover plants. Please could I have some advice on which of these plants are non toxic to goldfish in the pond. I had a bad experience a few years ago when I lost all my goldfish due to a Sedum plant that grew into the pond. When I cut it back the sap (like a white milk) from inside the stem ran into the pond and next day all the goldfish were dead. Any advice would be very much appreciated. Thank you, Tony

    • Hi Tony,

      Apologies for the delayed response!

      Ah, I’m sorry that you experienced that; that’s quite terrible!

      Would you mind telling me which hardiness zone you live in? That will give me a better idea of plants that will be better-suited for your area and climate. In the meantime, I’ll suggest a few shrubs that I think might work for you!

      1) Juniper species (genus Juniperus): There are over 60 juniper species, and none should be toxic to fish. In fact, a large variety of birds, mammals, and even fish dine on the berries. With so many species, there’s also a lot to choose from in terms of exact size and coverage, but any of them should do fairly well being planted amongst rocks and in drier conditions.

      2) Mountain camellia/mountain stewartia (Stewartia ovata): This one will grow anywhere between 10 and 15 feet tall typically, but takes many years to get there. It has deep green leaves, beautiful flowers, grows well in dry and rocky conditions (but does prefer a soil pH above 6, and can also be grown in damp soil), and isn’t known to be toxic to any animals, including fish. They’re also evergreen if you live above zone 6.

      3) Rosemary (Salvia rosmarinus): A great addition to dry, rocky areas that isn’t toxic to your fish, and you can also harvest for some herbs if you’d like! Or, leave as-is and enjoy the scent that the leaves naturally give off.

      4) Dog rose (Rosa canina): this is a rose species that, while it does still prefer soils more on the moist side, will tolerate drying out between waterings and might be alright planted amongst rocks. Dog rose is not considered toxic to fish or other animals, but one study did find that direct exposure to Rosa canina oil via rosehips increased some stress hormones in carp. Therefore, we’d just recommend cleaning out any rosehips that happen to fall into the pond. I’ve attached the study here, if you’d like to give it a read:

      5) Sempervivum species, also known as “hen and chicks”: these succulents are perfect for rockeries! As with other succulents, they require little water and do quite well in rocky, dry, well-draining locations. There are multiple varieties with slightly different leaf compositions and colors to choose from, and are non-toxic.

      I hope that this helps! Please let us know if you have any other questions.

  25. I am looking for information on whether camphor tree leaves and berries are toxic to koi and goldfish. Any info would b greatly appreciated. Thanks!

  26. Hi and thank you for the info in the article. I was wondering if ralf hedera helix, coleus, and hard rush were ok to do hydroponics on top of a fish aquarium? Thank you in advance.

  27. Lovely to read so much info on plants harmful to fish. Thank you ! I have a 3000 gallon raised pond with viewing window in England . I have some 40 and 50 year old koi raised from babies as well as young ones . There us no vegetation in or near my pond but I have a brilliant filter system and oxygen diffusers as well as a small waterfall. I skim the surface every day . Can I plant a passiflora alanta near it? I was hoping it would grow over the pump house adjacent to the pond/tank . Regards Janice

  28. Hi I have goldfish in large out door pond . No problems over the last 8 years and quite suddenly over last month the are dying . We emptied pond out and replaced with rain water leaving some of the water in pond and they still dying. They start by swimming erratically, side ways , upside down and have buoyancy problems.
    We thought maybe it was bloat belly, stop feeding them fish food and replaced with peas.
    They have no sign of disease or colouring.
    We had a resident small frog that had been in the pool for about 6 months, I thought maybe this was causing stress to fish , so took him out to another creek far away.
    But they still dying.
    I’ve added oxygen plants , we have a small water fountain that circulates water.
    Water test come back perfect?
    We have large fern trees that are near pond they sometimes drop leaves.
    Would it be something from surrounding pond .. plants , fern ??
    Please help

    • Hi McKenzie,

      Sorry about the late reply!

      After some digging, it looks like begonias contain a couple of compounds that have been known to be toxic in certain quantities to dogs and cats (primarily the compounds calcium oxalates and cucurbitacin B). I would encourage removing the flowers, just in case, as the goldfish could nibble at them or the flowers could release the compounds as they invariably begin to break down in the water.

    • Hi Graphic,

      Unfortunately, there is little information regarding pandan leaf toxicity relating to fish. However, it’s often fed to rabbits, various animals native to Malaysia (where the plant grows) eat it, and it’s a popular component of many Asian dishes. With that in mind, it is likely safe for your fish.

  29. Hi, I fed my goldfish rosemary I’m very worried about it being poisonous to my black moor goldfish. Is it ? I’ve only just fed him rosemary for the first time like 10 mins ago but some websites are saying it’s toxic to goldfish. If it is poisonous is there anything I can do other than not feeding him it again?

    • Hi Joss,

      Rosemary isn’t known to be toxic to animals like dogs, cats, or horses, but there is little to no research on its effect on fish. Just in case, I would refrain from feeding rosemary again in the future, just to be safe!


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