Help with floating fern

Help with floating fern

I’ve recently learnt that the introduced Azolla pinnata (ferny azolla) has been found in the Wellington region. I’m interested in its distribution and would be grateful for help in looking for more. Azolla plants are fairly easy to spot: look for a red plant covering still bodies of water.

Azolla plants often become red in full sunlight, and they can become so abundant that they carpet ponds, drains, and other still bodies of water. This is Azolla rubra in a pond on Mana Island, Wellington. Photo Leon Perrie. © Te Papa.

Azolla are ferns, believe it or not! They are free floating, and while individual plants are only a few centimetres across, they can proliferate in good conditions to ‘carpet’ large areas of water surfaces.

There are two species in New Zealand: the native Azolla rubra (Pacific azolla, previously known as Azolla filiculoides); and the exotic Azolla pinnata, which is an introduction from the tropics.

Azolla pinnata has largely replaced the native Azolla rubra in the northern North Island. It is therefore a concern that A. pinnata was found near Waikanae in recent weeks, after being found near Whanganui a few years ago. It seems it is continuing to spread south.

The introduced Azolla pinnata has very regular branching. Plants can be red or green depending on whether they are in the open or shade, respectively. The green ovals are Lemna duckweed (a flowering plant). Photo Leon Perrie. © Leon Perrie.
The branching of the native Azolla rubra is irregular. Photo Leon Perrie. © Te Papa.

Can you help please?

I would like to better document the distribution of the two Azolla species in New Zealand, and particularly the spread of the introduced A. pinnata. The southern North Island is the primary interest, but anything that adds to what we already know would be useful (see the link to the map below).

Map of Te Papa’s collections of Azolla.

If you see Azolla (either species), you could post a comment or send me an email. If you have landowner permission, you could make a collection for possible addition to Te Papa’s specimens: post me 20-30 plants enclosed within a watertight plastic bag, with locality details, and your contact details. My address is: Leon Perrie, Te Papa, PO Box 467, Wellington 6011.

Thanks very much.


  1. Kia ora Leon, I have a pond in Karitane, north of Dunedin, covered in what looks like this. Very beautiful close up. Green and red. I have horses near this pond and dogs who love a swim. A variety of ducks and pukeko live near. Is it harmful to animals? Thanks

  2. A drainage channel beside the Christchurch Northern Corridor (approx surface area 1600 sqm) is currently almost completely covered with Azolla rubra.

  3. I have just had a friend say that azolla absorbs a lot of carbon dioxide and could help with climate change?? Could this fern also be utilised as a cattle food and natural fertilizer for farmers to use.??

    1. Author

      Kia ora Rosalind. Yes, potentially. I believe it is already widely used as a natural fertiliser in rice paddies, thanks to the ability of the associated bacteria to fix nitrogen. The trick with any carbon-sequestration efforts will be to lock the carbon away. For instance, once the fern dies and decays, the carbon it had absorbed is released back into the environment/atmosphere.

  4. Hi we live near Arrowtown & we have Azolla Rubra in our pond. Tried to use it as compost & great mulch for roses over the years. This summer been abundant, trying to get rid of it is almost impossible. Our gold fish died in it & they form oil slicks which killed the azolla. Regards.

  5. We live in Peka Peka. 2 years ago I noticed this reddish weed on our 3/4acre (?) Pond. We have a deep, and exposed-surface, dark, peat water pond. Groundwater keeps it replenished. Previously pristine edge rushes, water lillies, and lots of frogs. Now this weed. I scoop it up with northerly wind assistance. It comes back. I just have to keep at it. I go out in a boat and scoop into buckets and compost. This blog is very interesting. I didn’t realise the weed was so recent! Cheers. Martin Phillips. Feel free to visit.

    1. Author

      Hi Martin. Thanks for your comment. Do you know whether your floating fern is the exotic species or the native species? The native species is still around in your area.

  6. Hi, I think I have Azolla in our dam in Northland, just outside of Dargaville. At the moment I’m not sure which one it is, but it is pretty aggressive in growth and has just about covered the entire dam. The dam isn’t sheltered in any way with nothing growing around it. I have only recently acquire the property and when I arrived (a year ago) there was nothing on the dam. This has only started in the last 2 months or so, but pretty much covers the dam now. Should I get rid of it (if I can), is it a noxious species, is it good for any of the wildlife around? What can I do? Thanks Kelly p.s would you like some samples?

    1. Author

      Hi Kelly,
      If it is the native species, the local wildlife would be well use to it. If it the introduced weedy species, then that is bad news for the native Azolla species (because it is being displaced), but I’m going to guess that most of the other local wildlife has probably not bein much affected. Although some people find Azolla unsightly, there is not much that can be done about it (other than scoop it up, and then it will just bounce back when conditions are good).
      If you’d like to know which species you have, you could upload a photo to
      And, yes, I would be grateful for a sample for Te Papa’s collections, if you can post me some in a sealed plastic bag to: Leon Perrie, Te Papa, PO Box 467, Wellington 6011. Thank you.
      Kind regards,

  7. Hi
    We are in Waitaheke Rd Te Horo adjacent to pateke-lagoons on Te Hapua Rd. We developed a new large lagoon/pond 9 years ago and the Azolla (A. pinnata) has been a developing problem. Our pond which is about .5 hectare is now covered in Azolla. Every year I have dredged it out but it returns in force the next spring. This is getting increasingly difficult to manage. The GWRC suggested more shade however this is difficult in such a large area which in newly developed. Do you have any suggestions?

    1. Author

      Hi Fergus,
      Sorry, but if you can’t make the habitat unsuitable for Azolla (by either shade, or, conversely, making it more exposed so the water surface is not calm), then as far as I know you’re struck with physical removal. I imagine that any kind of sprays will also be toxic to other life in the pond. And, even then, the Azolla will come back every year, as long as there are birds to disperse it between waterways.

    2. Leon I have come across Orange Oil which purportedly gets rid of azolla by making it heavy so it drops to the bottom. It comes from Australian company and purports to be safe for fish and aquatic wildlife

    3. Author

      thanks Deb. Looks interesting. I wonder how it goes with aquatic invertebrates.

  8. Can you give me any idea of how to get rid of the azzolla rubra in my pond please? Its just a thick carpet and I am concerned that my dragonflies and other insects wont be able to lay eggs in the pond. Also frogs could be compromised, let alone being afraid it will turn into a red stinking mess. Has it got a life cycle or are we condemned to a lifetime of trying to dredge it out?

    1. Author

      Hi Ann.
      Dredging is the way to go, I suppose.
      Azolla likes calm water, and you might be able to increase the rate it breaks up by making the water’s surface more exposed to wind (e.g., removing sheltering vegetation), but that could be difficult to get right.
      That said, it is a native species, and indigenous animals will be well used to living with it. It may look like an impenetrable carpet to humans, but it won’t be to invertebrates.
      Kind regards,

  9. Resident owners of our small lake in Paraparaumu have just had confirmed by DOC that the floating weed in our lake is the native Azolla Rubra. It is spreading fast and we’re looking into how to best control it so it doesn’t smother the lake to the detriment of the fish and eels.

    1. Author

      Hi Liz,
      Sorry for the slow reply – I’ve been away.
      Azolla rubra is part of the indigenous ecosystem, so I suspect the eels and other fish will be used to it.
      It probably expands during calm periods, and then is reduced in coverage when winds make the waters choppy.
      Kind regards,

  10. Hi Leon, earlier this year I observed a pond north of Masterton entirely covered in Azzola.
    The pond is about 2 acres in size.
    I will go back there next week and grab some specimens for ID and will advise you of species.

    1. Author

      Thanks very much Pete. I look forward to hearing which species you find near Masterton – hopefully the native species.
      You might like to upload a photo to the biodiversity-recording website:

      Thanks also for the link to the TradeMe auction. I have left a note for the seller, urging them not to sell/distribute Azolla pinnata if they care about New Zealand’s nature.

  11. Pretty sure there is azolla on lagoon at Muriwai. Is this of interest to you? I can get photos if you are but don’t have any currently.

    1. Author

      Hi Sally Lea. Yes, I would be interested in photos, so we can tell what species is there. The best place for the photos would be to upload them to the citizen science website; then your observation becomes data that anyone can use. Or you could email them to me –

  12. We have Azolla in Travis Wetland Reserve in Christchurch. Im almost definitely sure that they’re Azolla rubra as my park ranger project manager who works there said that they are the native Azolla. They’re quite abundant around the boardwalk areas that are boggy and swampy. I don’t think Ive seen any Azolla pinnata but I’ll have a closer look tomorrow

    1. Author

      Hi Juliet,
      Thanks for that observation. Feel free to send me pictures for confirmation and/or post them to NatureWatch ( for ‘crowd-sourced’ identification.
      Kind regards, Leon

  13. I have just cleaned out masses of oxygen weed from my garden pond and with it the covering of azolla. I am pretty sure it is rubra. With the oxygen weed gone the pump is working more efficiently and the azolla is somewhat more inhibited. I am just off SH1 on the north eastern side of Otaki.

    1. Author

      Hi Elizabeth,
      Thanks for the report. Good to know the native species is still around.

  14. HI leon

    There is heaps of A. pinnata in our ponds in Te Hapua Rd, Te Horo. I have been searching for A. filliculoides but can’t seem to find any. You are welcome to visit. See our website

    Kind regards, Adrienne

    1. Author

      Thanks Adrienne. We’ve had sightings from near there. Next time I head north, I might take you up on the offer to visit, as I would be interested to see how established the A. pinnata is. I would be interested to know if you do find A. rubra/filiculoides at your place, or if you see A. pinnata elsewhere.
      Kind regards, Leon

  15. Note: the scientific name of the native species updated in this post to Azolla rubra from A. filiculoides, 2 April 2013.

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