Native to Brazil, Salvinia molesta is a free-floating aquatic fern. One of several species of salvinia that occur naturally in America, Europe and Asia, it is the only salvinia species to become established in Queensland. It is also found in New South Wales and the Northern Territory.

Salvinia forms thick mats that can quickly cover water bodies. Infestations reduce water flow, degrade water quality, and affect native animals, stock, and recreational users.


Scientific name

Salvinia molesta

Other names

Giant salvinia

Similar species

  • Other salvinia species


  • Free-floating aquatic fern.
  • Small green leaves are positioned in pairs along a common stem.
  • Leaf surfaces are covered with long, stiff, water-repellent hairs, joined at the tip to form eggbeater-like shapes.
  • As the plant matures, leaves become thick and fold at mid-rib.
  • Young leaves are oval, about 12mm across, lie flat on water, often resembling duckweed.
  • Roots trail from each pair of young leaves.


  • Prefers slow-moving streams or still-water ponds with high nutrient levels and water temperatures 20-30oC.

Distribution in Queensland

  • Found in isolated water bodies from north Queensland to the New South Wales border, and west to Mt Isa.

Life cycle

  • Believed to be a sterile hybrid.
  • Does not produce flowers, reproducing by vegetative means.
  • Produces little growth in winter.
  • Under optimal conditions, can double in volume every 2-3 days.



  • Forms thick mats that can quickly cover water storage areas.
  • Degrades water quality.
  • Destroys wildlife habitats.


  • Builds up and collects debris during flooding, causing bridges and fences to collapse.
  • Reduces water flow to irrigation equipment, increasing pumping times and costs.
  • Prevents access by stock to drinking water.


  • Endangers children and livestock, who can become entangled in heavy infestations.
  • Creates mosquito-breeding habitat.
  • Interferes with recreational activities such as boating, fishing and swimming.
  • Spoils natural beauty of open water bodies such as dams and lakes.

How it is spread

  • Mainly spread by people emptying aquariums and ponds into waterways.
  • Also spread by water currents and fouling of fishing equipment and boat trailers.


Mechanical control

  • Removal by hand or machine is a practical control method often used for small areas, or when weed numbers are low.
  • Mechanical control can take advantage of flooding or water flushes that deposit salvinia in dams, lagoons and calm waters of rivers and creeks. When using this method, it is essential to remove salvinia before rapid growth commences.
  • Salvinia can survive for long periods out of water when it is deposited on moist banks. To help prevent its re-introduction into a watercourse, move it away from the water's edge and, preferably, burn it.

Herbicide control

  • Herbicides are effective.

See the Salvinia fact sheet (PDF, 519KB) for herbicide control and application rates.

Biological control

  • The salvinia weevil Cyrtobagous salviniae has been extensively released. In Queensland, can give good biological control.
  • The salvinia weevil is 2-3mm long and dark brown to black. It is most effective when air temperatures are 27-35˚C and salvinia nitrogen levels are high.
  • Salvinia weevil larvae feed on new growth buds and tunnel into the rhizome. Tunnelling weakens the salvinia, reducing its ability to grow and compensate for bud loss. Adult weevils also affect plant growth by feeding on buds.
  • In the initial stages of weevil damage, some salvinia leaves will turn brown. As salvinia weevils continue their control efforts, the whole mat will turn brown, sink and decompose.
  • Although effective in tropical areas, the salvinia weevil is not establishing as intensely in cooler southern areas of Queensland and may take several years to control infestations there.
  • Depending on infestation size and environmental conditions, time taken for weevils to control salvinia varies from 13 years. They may take more than five years to establish in cooler areas.
  • To ensure maximum build up, it is best to release salvinia weevils in spring. When releasing weevil-infested salvinia, it is essential to choose warm, sunny positions where a drop in water level will not leave the salvinia stranded.
  • To establish an effective breeding population of weevils, infested plants should be placed in an area where salvinia is concentrated.

Declaration details

  • All other species not yet found in Queensland are declared Class 1 species.
  • A declared Class 2 species under the Land Protection (Pest and Stock Route Management) Act 2002.
  • Taking for commercial use, introduction, keeping, releasing and supplying (including supplying things containing reproductive material of this pest) is prohibited without a permit issued by Biosecurity Queensland.
  • Landholders are required to control declared pests on their properties.

More information

Contact us

Call your local government office, or Biosecurity Queensland on 13 25 23.

Last updated
25 November 2015