Elodea (Elodea canadensis)

Elodea is a submerged water weed with long stems and whorls of small, leaves. Dense infestations of Elodea outcompete native plants, reducing food and habitat for native fish.

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How does this weed affect you?

Elodea forms dense mats under the water that:

• reduce water capacity and flow in irrigation channels
• outcompete native plants
• reduce food and habitat for fish and other aquatic animals
• make recreational activities such as swimming, fishing and boating difficult.

What does it look like?

Elodea is a perennial, submerged water plant, usually anchored in the mud.  Plants grow in water up to 5 m deep. It forms thick green masses at, and just below, the water’s surface. Plants are either male or female. However, only male plants have been found in Australia.

Leaves are:

• bright green
• 5–20 mm long and 1–5 mm wide
• in groups of 3 (rarely 4 or 5) arranged in whorls around the stem
• usually minutely toothed along the edges, occasionally smooth
• often bent down slightly
• stalkless.

Flowers:

• are whitish and difficult to see
• 3–5 mm in diameter
• have three petals
• float on the end of white, thread-like stems (2–20 cm long)
• are present mostly in spring and summer.

Only male flowers have been observed in Australia.

Fruit are:

• not yet present in Australia
• up to 9 mm long and 3 mm in diameter
• egg-shaped and beaked containing 1–6 seeds.

Stems are:

• usually up to 3 m long, sometimes up to 6 m long
• brittle at the joints
• branched.

Roots are:

• long, white (sometimes red) and threadlike
• grow from the stem nodes near the base of the plants
• anchored in the bottom of the waterway.

Similar looking plants

Elodea looks like:

• Leafy elodea (Egeria densa), which has larger leaves (up to 4 cm long) and larger flowers (2 cm across). Its leaves are usually in whorls of 4 or 5.
• Hydrilla (Hydrilla verticillata), which has larger dull green leaves (up to 4 cm long) that are almost straight.
• Lagarosiphon (Lagarosiphon major), which has alternate spirals of leaves instead of rings. The leaves are strongly curved backwards.

Where is it found?

In NSW, Elodea has been found in the Northern Tablelands, Hunter, Greater Sydney and South East regions.

It is native to North America and was sold in Australia as an aquarium plant.

What type of environment does it grow in?

Elodea grows in temperate climates and can survive freezing conditions. Plants grow quickly in slow-moving and stationary water, with full sun when temperatures are over 15 °C. Most plants are found in fresh water, but Elodea can also survive in slightly brackish water.  Plants grow slowly in shade and in water with low iron content. They can grow in fast-flowing waters but do not form dense masses.

 Elodea grows in:

• irrigation channels
• dams and ponds
• lakes
• creeks and rivers (mostly slow flowing).

How does it spread?

By plant parts

Elodea spreads by broken stem fragments. The long stems easily break into pieces and are moved by flowing water. Plants can also be spread by people dumping water and plants from ponds or aquariums.

References

Regional NSW. (2023). Recognising water weeds: plant identification guide. Second Edition. NSW DPI.

Identic Pty Ltd. and Lucid Central (2016). Environmental Weeds of Australia Fact sheet: Elodea canadensis Michx. (Roxb. ex Rottler) Roxb. Retrieved 27 November 2027 from: https://keyserver.lucidcentral.org/weeds/data/media/Html/elodea_canadensis.htm

Martemyanov, V. I., & Tikhonenkov, D. V. (2022). Assessment of the tolerance range of salinity for invasive waterweed Elodea canadensis Michaux by parameters of water-salt homeostasis. Biological Invasions, 24(12), 3845-3853.

Parsons, W. T. and Cuthbertson, E. G. (2001) Noxious Weeds of Australia. 2nd Edition. CSIRO Publishing, Collingwood.

PlantNET (The NSW Plant Information Network System). Royal Botanic Gardens and Domain Trust, Sydney. Retrieved 27 November 2024 from: https://plantnet.rbgsyd.nsw.gov.au/cgi-bin/NSWfl.pl?page=nswfl&lvl=sp&name=Elodea~canadensis

Sainty, G. R. Jacobs, S. W. L. (2003) Waterplants in Australia. 4th edition. Sainty and Associates, Potts Point.

More information

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Control

Prevention

To prevent the spread of Elodea:

• Do not run boat motors or paddle through water weeds.
• Check and remove all plant material from boats, canoes, trailers, vehicles, machinery and fishing gear before leaving waterways.
• Stop nutrient-rich runoff entering infested waterways.
• Never dump unwanted water plants.

Early detection is important in managing Elodea. Check waterways regularly.

Physical removal

Cutting, hand pulling, cultivating, or using draglines and booms can contain or temporarily remove Elodea. These methods may be expensive and risk increasing spread by dispersing fragments. It is difficult to remove all fragments, and regrowth is likely.

Lowering water levels

If possible, completely drain channels or small dams and allow the bed to dry out. This can give effective control in sunny, windy weather and may also be effective with frost. Ensure that Elodea is not spread to other areas in the drained water.

Shading

Shade can reduce the growth rate considerably. In small dams or ponds, a cover (such as black plastic or shade cloth) can be placed over the waterway. In natural areas, revegetating riparian areas with native plants can increase the shade.

Disposal

Contact your local council for advice on how to dispose of this weed.

Chemical control

In some circumstances herbicides can be injected into the water. Read the herbicide labels for appropriate situations and methods.

Herbicide options

See Using herbicides for more information.

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Diquat 200 g/L with (Various products)
Rate: 5 L per Megalitre of water
Comments: Apply by injection below the surface or as a surface spray. Follow label as for pond weeds.
Withholding period: Do not use treated water for human consumption, livestock watering or irrigation purposes for 10 days after application. Do not graze or cut sprayed vegetation for stock food for 1 day after application. See label for harvest withholding periods.
Herbicide group: 22 (previously group L), Inhibition of photosynthesis at photosystem I via electron diversion (PSI electron diversion)
Resistance risk: Moderate

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Biosecurity duty

The content provided here is for information purposes only and is taken from the NSW Biosecurity Act 2015 and its subordinate legislation, and the Regional Strategic Weed Management Plans (published by each Local Land Services region in NSW). It describes the state and regional priorities for weeds in New South Wales, Australia.

Area	Duty
All of NSW	General Biosecurity Duty All pest plants are regulated with a general biosecurity duty to prevent, eliminate or minimise any biosecurity risk they may pose. Any person who deals with any plant, who knows (or ought to know) of any biosecurity risk, has a duty to ensure the risk is prevented, eliminated or minimised, so far as is reasonably practicable.

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Reviewed 2024