Aquatic weeds

Propeller heavily fouled in aquatic vegetation

Aquatic weeds include freshwater plants such as Salvinia, Cabomba and alligator weed.

Aquatic weeds can seriously harm the environmental and recreational value of rivers, estuaries and lakes. These weeds are often highly invasive and can smother and choke water bodies by forming large floating mats, dense submerged thickets or stands along the bank.

A single infestation of Salvinia once smothered 80 kilometres of the Hawkesbury River.

Aquatic weeds can deplete oxygen levels, reduce sunlight penetration and displace native plants. The associated effects on water quality and available habitat can reduce the abundance and diversity of fish and other aquatic animals and displace waterbirds. In some cases, boating restrictions are required to minimise the spread of aquatic weeds, while heavy infestations can make boating impossible.

These weeds can be spread in a variety of ways. Propellers and anchors can cut plants into fragments that are then easily spread by currents. Fragments can be introduced to new water bodies via vessels, trailers and fishing equipment. A single plant fragment can start a new infestation, and some weeds can survive for several days out of water, especially in damp conditions amongst ropes, diving equipment and fishing gear etc.

If you are boating in a Caulerpa infested area or on freshwater rivers, lakes and dams you should:

  • Avoid shallow weedy areas or places with heavy aquatic plant growth where possible
  • Obey any local vessel exclusion zones or fishing closures
  • Inspect all ropes, anchors and fishing gear before and after use
  • Clean your boat, trailer and all equipment after removal from the water and before moving to another waterway
  • Learn to recognise aquatic weeds and be observant for new or unusual weeds.

If you suspect a new weed infestation in freshwaters, contact your local council weed officer or the NSW Department of Primary Industries (DPI) on 1800 680 244 or email Further information on freshwater weeds can be found on the Pest and weeds management page of the DPI website.

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