Egeria (Dense Water Weed)

(Egeria densa)
Image: Egeria stem, © Stephen Welsh

What is egeria?

  • Egeria is a weed of freshwater ponds, lakes, reservoirs and slow moving streams.
  • Egeria is a declared weed in Tasmania under the Tasmanian Weed Management Act 1999. The importation, sale and distribution of egeria are prohibited in Tasmania.

How to identify egeria

  • Egeria is a submerged, perennial (long-lived) freshwater herb, the stems of which may grow to 5 m long. Egeria is usually firmly rooted in the bottom mud, but may occur as a free floating mat near the water surface.
  • The stems are green to brown in colour, much branched, and bear whorls of strap-like leaves which become densely clustered together on the middle and upper stem. The flowers are large, white and unisexual. Plants are either male or female; only male plants occur in Australia.
  • Stem growth begins as water temperature rises above 15oC, and a thick mat of intertwining stems forms below the water surface. Flowering is in early summer.
  • For further help in identifying egeria, search the Dennis Morris Weeds and Endemic Flora database for egeria illustrations. If you are still in doubt about the weed you are dealing with, contact Biosecurity Tasmania on 03 6165 3777 for help.

Egeria in Tasmania

  • Egeria is recorded as an occasional weed of ponds and slow moving streams in Tasmania. Egeria is also occasionally found in aquaria.
  • Egeria is a serious weed in a variety of freshwater environments, reducing water flow and interfering with recreational activities, hydro-electric operations and irrigation.

What is the legal status of egeria in your area?

Detailed management and control guidelines for egeria can be found in the Egeria Control Guide. Refer also to Herbicides for Aquatic Weed Control. For further information see Weed Links and Resources.

See also

Herbicides for Aquatic Weed Control
Statutory Management Plan for Egeria
Weed Links and Resources

Other useful links
Pest Genie

Egeria Control Guide


  • Plan your control program, this will save time and money in the long-run;
  • Consider the impact of your control methods on off-target species, especially if herbicides are used;
  • Get in early - For new infestations, eradicate before the plants reach the flowering stage: once plants begin seeding, control becomes more difficult and expensive;
  • Carefully time your use of herbicide for best results (see the Herbicides for aquatic weed control link for more information);
  • Coordinate your control program with neighbouring landholders where your weed problem crosses property boundaries;
  • Revisit and regularly inspect the site and ensure follow-up is undertaken.


  • Don't start your control program without first planning your approach;
  • Don't allow an infestation to become established. Get in early!
  • Don't rely on just one treatment: follow-up is essential.

Spread of egeria

  • Only male plants occur in Australia, and all reproduction is vegetative. Infestations of egeria increase in size when the over-wintering colony begins new growth in spring.
  • New colonies are formed when stem fragments break away from the colony in stream flow and establish downstream. Egeria also continues to be spread in the aquarium trade.

Physical removal

  • Hand pulling, cutting and digging with machinery is not effective in controlling egeria.
  • Physical removal provides only temporary reduction of an infestation, and can encourage spread of the weed by stem fragments.

Chemical control

Herbicides for Aquatic Weed Control

Herbicides for Aquatic Weed Control

Important Disclaimer

To the extent permitted by law, the Department of Natural Resources and Environment Tasmania (including its employees and consultants) excludes all liability to any person for any consequences, including but not limited to all losses, damages, costs, expenses and any other compensation, arising directly or indirectly from using information or material (in part or in whole) contained on this website.​