Biosecurity Spotters logo

Frogbit (Limnobium laevigatum)

Frogbit is a fast-growing floating freshwater weed that is prohibited matter in NSW and must be reported if found. It forms dense mats that can damage aquatic habitats and block waterways.

Key facts

Type: Weed, aquatic.

Native to: Central and South America.

Established in: QLD, NSW, VIC, WA.

Other names: Hydrocharis laevigata.

Identification

  • Frogbit is a perennial floating waterweed with bright green, glossy leaves, usually rounded at the tip and up to 6 cm long and 4 cm wide.
  • Young leaves are round, spongy underneath and float flat on the water; mature leaves become more oval and can extend up to 50 cm above the water.
  • Its flowers are about 13 mm wide and white, greenish-white or yellowish.
  • Short, mostly branched stems bear leaves, while unbranched runners up to 50 cm long produce a daughter plant at the end.
  • Hairy roots anchor the plant in substrate where water is less than 30 cm deep.
  • Look-alike: Spongeplant (Limnobium spongia) has larger fruit and usually pointed leaf tips; it is also prohibited matter but is not yet known to occur in Australia.
  • Look-alike: Water poppy (Hydrocleys nymphoides) has yellow flowers up to 8 cm wide and leaves up to 12 cm wide; the native frogbit (Hydrocharis dubia) has flowers 2–3 cm across with three round white petals and yellow centres.

Where it grows

In NSW, naturalised and cultivated plants have been found in Greater Sydney, Hunter, South East, North Coast, Northern Tablelands, Central Tablelands and the Western region, growing on freshwater rivers, ponds, dams, lakes, canals and other aquatic habitats.

Why it matters

  • Dense mats outcompete native water plants and reduce light, food and shelter for fish and other aquatic animals.
  • Frogbit can block waterways and irrigation channels and make water appear like firm ground, creating dangerous conditions.
  • It can limit fishing, swimming and boating, and increase suitable habitat for mosquito breeding.

How it spreads

  • Illegal dumping of aquarium or pond plants in waterways has been the main cause of infestations in NSW.
  • Seeds can remain viable for at least 3 years; they are released from fruit, germinate underwater and float to the surface.
  • Seeds and plant parts can be moved by water flow, wind, birds, watercraft or equipment; daughter plants also spread within a waterbody.

Control options

  • Do not attempt to treat or dispose of Frogbit yourself.
  • Report any Frogbit found in NSW immediately by calling the NSW Biosecurity Helpline on 1800 680 244.
  • NSW DPIRD, Agriculture and Biosecurity will lead the initial response for treatment and disposal.

Hygiene and washdown

  • Do not dump aquarium or pond plants into waterways, and avoid moving Frogbit or plant parts between waterbodies on watercraft or equipment.
  • 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, categories 3, 5. Do not give it away, sell or release it into the environment; do not keep it. Everyone must also take all reasonable and practical steps to minimise its risks (the general biosecurity obligation).
  • New South Wales: Prohibited matter. It is an offence to deal with it, and you must notify NSW DPIRD as soon as you become aware of it.
  • 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 (no control category). Declared pest in WA without a control category, so there is no state-wide control requirement, but movement and keeping rules can still apply.
  • Tasmania: Not declared. Not a declared weed in Tasmania. Other laws may still apply.
  • Northern Territory: Declared weed, Class C. Class C: must not be introduced to the NT.
  • 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
  • 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

Sources