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Water lettuce (Pistia stratiotes)

A floating rosette plant that forms thick mats on dams, lagoons and slow rivers, much like water hyacinth.

Key facts

Type: Weed, aquatic.

Native to: Tropical regions worldwide.

Established in: QLD, NSW, NT.

Identification

  • Floating rosette of thick, velvety, pale green leaves with ridged veins, like a small lettuce.
  • Long, feathery roots hanging in the water.
  • Connected by runners to daughter plants.

Where it grows

Still or slow-flowing fresh water.

Why it matters

  • Blocks light and lowers oxygen levels.
  • Blocks pumps and access.

How it spreads

  • Plantlets and seed moved by water, boats and aquarium dumping.

Control options

  • Physical removal of small infestations.
  • Herbicides permitted for aquatic use.
  • A weevil biological control agent is used in some areas.

Hygiene and washdown

  • Check, clean and dry boats, trailers and gear.
  • 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): No national listing. Managed under state and territory law.
  • 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: Regional priority in 9 of 11 regions. Regional priority weed in Greater Sydney, Hunter, Murray, North Coast, North West, Northern Tablelands, Riverina, South East, Western. The general biosecurity duty applies: anyone dealing with it must prevent, eliminate or minimise the risk it poses.
  • Victoria: Not declared. Not declared under the Catchment and Land Protection Act 1994. Other Victorian laws may still apply.
  • South Australia: Not declared. Not declared under the Landscape South Australia Act 2019. Other laws may still apply.
  • Western Australia: Declared pest (C2). C2 Eradication: present in limited areas and targeted for eradication.
  • Tasmania: Not declared. Not a declared weed in Tasmania. Other laws may still apply.
  • Northern Territory: Check NT list. There is no NT weed profile for it. Check the NT declared weeds list for its current status.
  • Australian Capital Territory: Declared pest, notifiable, prohibited. It is a declared pest throughout the ACT. You must report it to ACT Biosecurity. 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
  • Northern Territory: Territory Parks and Wildlife Conservation Act 1976 (NT), administered by NT Department of Lands, Planning and Environment

Sources