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Water hyacinth (Pontederia crassipes (formerly Eichhornia crassipes))

A floating aquatic plant with showy flowers, often called the world's worst aquatic weed. It covers dams and rivers, reduces oxygen and blocks infrastructure.

Key facts

Type: Weed, aquatic.

Native to: South America.

Established in: QLD, NSW, VIC, WA, NT.

Identification

  • Free-floating plant with glossy, rounded leaves on swollen, spongy stalks.
  • Spikes of lavender to blue flowers, the upper petal with a yellow spot.
  • Feathery dark roots trailing in the water.

Where it grows

Still or slow-moving fresh water, including dams, lagoons, rivers and drains.

Why it matters

  • Covers water bodies and lowers water quality.
  • Blocks pumps, weirs and drainage.
  • Breeding habitat for mosquitoes.

How it spreads

  • Plantlets and seeds moved by water, people and machinery.
  • Pond and aquarium trade.

Control options

  • Physical removal of small infestations.
  • Herbicides permitted for aquatic use.
  • Biological control weevils and moths in warmer areas.
  • Long-term follow-up, as seed survives many years in sediment.

Hygiene and washdown

  • Check, clean and dry boats, trailers and pumps.
  • Inspect and clean vehicles, plant and footwear before leaving an infested area, paying attention to tyres, radiators, belly plates, tracks and floor mats.
  • Wash down at a designated bay where runoff is contained and can be monitored for seedlings.
  • Record each washdown so the client has evidence of clean entry and exit.

Classification by state

  • Australia (national): Weed of National Significance. One of 32 nationally agreed priority weeds, managed through national strategies with all states and territories.
  • Queensland: Restricted matter, category 3. Do not give it away, sell or release it into the environment. Everyone must also take all reasonable and practical steps to minimise its risks (the general biosecurity obligation).
  • New South Wales: Biosecurity zone; Sale prohibited; Regional priority in 3 of 11 regions. A biosecurity zone applies in parts of NSW, with mandatory control inside the zone. It must not be imported into NSW or sold anywhere in the state. Regional priority weed in Greater Sydney, Hunter, North West. The general biosecurity duty applies: anyone dealing with it must prevent, eliminate or minimise the risk it poses.
  • Victoria: State prohibited weed. State prohibited weeds are the highest priority: the Victorian Government is responsible for eradicating them, so report any sighting to Agriculture Victoria.
  • South Australia: Declared plant. Depending on the declaration, it can be an offence to move it on public roads or sell it, and landowners may be required to control it on their land.
  • Western Australia: Declared pest (C2), prohibited. C2 Eradication: present in limited areas and targeted for eradication. It must not be brought into WA (prohibited organism).
  • Tasmania: Declared weed. Property managers are required by law to control declared weeds, and their import and sale are prohibited.
  • Northern Territory: Declared weed, Class A. Class A: to be eradicated. All declared weeds are also Class C, so they must not be brought into the NT.
  • Australian Capital Territory: Declared pest, prohibited. It is a declared pest throughout the ACT. Dealing with it, such as selling, moving or keeping it, is prohibited.

Legal obligations

Every state and territory places a duty on landholders and people working on land to prevent the spread of invasive species, such as the general biosecurity obligation in Queensland and the general biosecurity duty in New South Wales. Declarations and control requirements differ between states and local government areas, so check the current official list before work starts.

  • Queensland: Biosecurity Act 2014 (Qld), administered by Biosecurity Queensland (13 25 23)
  • New South Wales: Biosecurity Act 2015 (NSW), administered by NSW Department of Primary Industries and Regional Development
  • Victoria: Catchment and Land Protection Act 1994 (Vic), administered by Agriculture Victoria
  • Western Australia: Biosecurity and Agriculture Management Act 2007 (WA), administered by the WA Department of Primary Industries and Regional Development
  • Northern Territory: Territory Parks and Wildlife Conservation Act 1976 (NT), administered by NT Department of Lands, Planning and Environment

Sources