About water hyacinth
Water hyacinth (Pontederia crassipes; synonym Eichhornia crassipes) is a freshwater plant that grows as a free-floating rosette of shiny, rounded leaves. The bulbous swelling at the base of each leaf stalk is characteristic of water hyacinth. The swelling and the rosette arrangement of the leaves are less obvious when the plants become very tall, with leaves up to about a meter tall.
The plants form mats held together by floating horizontal stems and thick masses of feathery roots hanging in the water. The roots are dark-coloured and can reach 2 m in length. Water hyacinth produces clusters of distinctive mauve-blue flowers, each with a yellow spot.
Why we don't want water hyacinth in New Zealand
Water hyacinth is one of the world’s most damaging aquatic weeds. It forms dense mats that can completely smother large waterways and severely affect water quality. These mats can create a drowning risk for people and animals. Water hyacinth infestations can also severely affect water quality, smother or force out native plants, attract breeding mosquitoes, remove oxygen from the water, and block dams and irrigation systems.
Where water hyacinth has been found in NZ
Water hyacinth has been recorded in many locations in New Zealand, mostly in the warmer regions of the North Island.
Water hyacinth eradication programme
Water hyacinth is one of the species being eradicated through the National Interest Pest Responses programme. The eradication programme includes containment of known infestations at a site to prevent further spread, site treatment (which can be manual removal of plants or herbicide application) and monitoring until eradication can be declared. Due to the longevity of the seeds, a site is monitored until it has been clear of plant material for 30 consecutive years to ensure no viable seeds remains.
Biosecurity New Zealand works closely with the regional councils, the Department of Conservation, and other organisations to eradicate water hyacinth from New Zealand.
National Interest Pest Responses programme
What to do if you find water hyacinth
Water hyacinth is an Unwanted Organism under the Biosecurity Act (1993). Propagation, spread, display, and sale are all prohibited. It is also a Notifiable Organism, which means you must report all sightings to the Ministry for Primary Industries.
If you think you have found water hyacinth:
- freephone our pest and disease hotline on 0800 809 966
- don’t touch the plants or try to remove them
- take photos and leave the plants so they can be treated or removed safely without spreading them further
- don’t tip the content of your aquarium or pond into a waterway as this could start another infestation with potentially serious consequences.
What water hyacinth looks like
