Dense waterweed

• Submersed aquatic plant growing up to 4m below water surface, with stems that can be more than 2m.
• Roots attach firmly to silt or soil.
• Leaves are up to 4cm long with tiny serrations on margins, grow in whorls of 4 or 5 (up to 8), mostly densely clustered at branch ends near growing tips.
• Flowers are 2cm in diameter and have 3 white petals.

• Found in flowing and standing water bodies.
• Prefers clear water.

• Large infestation in Lake Baroon on Sunshine Coast.
• Found in some South East Queensland creeks.
• Not known to be widespread in Queensland.

• Reproduces mainly through stem fragments.

Environmental

• Forms dense, submerged masses that can seriously hinder water flow.
• Displaces native aquatic plants.

Economic

• Interferes with irrigation equipment, hydro-electric activity and potable water supplies.

Social

• Impedes fishing, boating and swimming.

• Spread by stem fragments through water currents and humans.

• Find out how farmers can prevent weed spread.
• Find out how gardeners and outdoor enthusiasts can prevent weed spread.

Physical control

• Hand-pulling, cutting and digging with machines can be effective.
• All methods need to be thorough to prevent regrowth from pieces.
• Infestations should be controlled while small.

Herbicide control

• No herbicides registered.

• Dense waterweed is not a prohibited or restricted invasive plant under the Biosecurity Act 2014. However, by law, everyone has a general biosecurity obligation (GBO) to take reasonable and practical steps to minimise the risks associated with invasive plants under their control.
• Local governments must have a biosecurity plan that covers invasive plants and animals in their area. This plan may include actions to be taken on Dense waterweed. Some of these actions may be required under local laws. Contact your local government for more information.