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 (NPPA)
The NPPA is designed to prevent the sale, distribution and propagation of a set list of pest plants (the Accord list) within New Zealand. If allowed to spread further, these pest plants could seriously damage the New Zealand economy and environment.
More informationUnwanted 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.
National Interest Pest Responses programme (NIPR)
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
Some organisms must be notified to MPI if they're spotted in New Zealand. These include serious pests and diseases like foot-and-mouth disease, the rabies virus, fruit fly and disease-carrying mosquitoes. If a notifiable organism established in New Zealand, it could severely affect our primary production or 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.
The Biosecurity (Notifiable Organisms) Order 2016 lists notifiable organisms. New additions can be made by the Governor-General and MPI periodically reviews the list to ensure it is up-to-date.
Taxonomies
FamilyPontederiaceae
TypePlants
GroupFloating
HabitatFreshwater
Management ProgrammeNational Pest Plant Accord (NPPA)Unwanted OrganismNational Interest Pest Responses programme (NIPR)Notifiable Organism
