What does it look like?
Water hyacinth is a free-floating aquatic plant that forms dense mats on the water’s surface. Its glossy, green, leathery leaves can be up to 8 cm wide, supported by swollen, spongy leaf stems that act as natural floats. Each plant features a mass of purple roots submerged below the surface. It produces striking spikes of up to ten large lilac-mauve flowers, each marked with a distinctive yellow spot at the centre of one petal.
Water hyacinth thrives in still or slow-moving freshwater habitats such as ponds, streams, swamps, and dams. In New Zealand, it is most commonly found in small, nutrient-enriched waterbodies.
Why is it a problem?
Water hyacinth forms dense mats that can completely smother waterways and degrade water quality. These mats exclude native plants, block dams and waterways, impede drainage, and disrupt recreational activities. While water hyacinth is generally frost-tender, dense mats can tolerate moderate frosts.
The plant reproduces from seeds that can remain viable for up to 20 years. It also spreads vegetatively, and new plants can grow from roots and can produce seeds within just 3 to 4 weeks.
Control methods
The water hyacinth eradication programme includes containment of known infestations and treatment or physical removal to eradicate the plants. Due to the longevity of the seed, sites are monitored for a total of 20 years subsequent to no detections, to ensure elimination of the infestation.
More information
If you think you have found water hyacinth, please call MPI’s Pest and Disease Hotline at 0800 80 99 66.
Related links
- https://niwa.co.nz/sites/default/files/Freshwater%20invasive%20species%20of%20New%20Zealand%202020_1.pdf
- http://apps.mpi.govt.nz/applications/nzpests-view/Article/530/Water-Hyacinth
- http://www.nzpcn.org.nz/flora_details.aspx?ID=3857
- https://www.mpi.govt.nz/biosecurity/long-term-biosecurity-management-programmes/national-interest-pest-responses-programme
- http://www.nzflora.info/factsheet/Taxon/Eichhornia-crassipes.html
- https://www1.maf.govt.nz/uor-cgi/uor.pl/show?species_id=21752
- https://www.weedbusters.org.nz/what-are-weeds/weed-list/water-hyacinth
- NPPA and the control of weeds | NZ Government
- How you can help get rid of water hyacinth
Notify Council
If you think you've found this pest, please get in touch with our Biosecurity Team at biosecurity@hbrc.govt.nz or call us on 0800 108 838.
Management Programme
National Pest Plant Accord
All plants on MPI's National Pest Plant Accord (NPPA) are unwanted organisms under the Biosecurity Act 1993 whose formal or casual trade contributes significantly to their spread.
Plants on the Accord cannot legally be propagated, distributed, or sold in New Zealand. If allowed to spread further, these pest plants could seriously damage our economy and environment.
Unwanted Organism
An unwanted organism is any organism that's capable of causing harm to natural or physical resources (like forests and waterways) or human health. A number of introduced pests in New Zealand are classed as unwanted.
More informationNational Interest Pest Responses programme
Nine harmful weeds are managed under the National Interest Pest Responses (NIPR) programme. These pests could cause serious harm to New Zealand's environment and economy if they are allowed to spread.
More informationNotifiable Organism
Any organism specified under the Biosecurity Notifiable Organisms Order 2016 must be reported to MPI if spotted. If any of these organisms become established in New Zealand, they could severely affect our primary production, trade, and market access. If you spot a notifiable organism, you have a legal obligation under section 44 of the Biosecurity Act 1993 to tell MPI. Call the pests-and-diseases hotline on 0800 80 99 66.
More informationRules
Section 26ZM of the Conservation Act (1987)
In accordance with the Conservation Act 1987 section 26ZM, no person shall transfer live aquatic life or release live aquatic life into any freshwater. This includes native or introduced fish, plants, and invertebrates. The taking and holding of some organisms requires a special permit from MPI.
More informationTaxonomies
FamilyPontederiaceae
TypePlants
GroupFloating
HabitatFreshwater
Management ProgrammeNational Pest Plant AccordUnwanted OrganismNational Interest Pest Responses programmeNotifiable Organism
