Water hyacinth (Eichhornia crassipes)

Water hyacinth is a floating water weed with blue flowers. It forms dense mats that reduce water quality, block irrigation channels and affect native aquatic life.

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How does this weed affect you?

Water hyacinth smothers the surface of waterways, dams, irrigation channels and drains. It can rapidly take over an entire waterway and under favourable conditions it can double its mass every 5 days. It:

• reduces water levels
• reduces water quality
• causes changes in water temperature and pH
• lowers oxygen levels 
• reduces the amount of sunlight under the water.

 The large infestations of water hyacinth impact negatively on agriculture and infrastructure by: 

• blocking irrigation channels and equipment
• reducing the quality of drinking water for livestock
• restricting livestock access to water
• damaging pastures and crops when masses of the plant settle in a paddock after floods
• damaging fences during floods
• blocking roads, bridges and culverts when masses of the plant become mobile during floods.

Water hyacinth also has negative impacts on people and the environment because it:

• restricts birds and other native animals’ access to water
• prevents native water plants from growing
• limits movement of aquatic animals
• reduces food and shelter for fish and other native animals
• provides favourable conditions for mosquitoes to breed
• prevents boating and water sports
• reduces the visual appeal of waterways.

What does it look like?

Water hyacinth is a floating water plant. In cool areas, the leaves die off during frosts but the crowns survive and regrow the following spring. 

Leaves:

• are bright green, sometimes rusty yellow on their edges
• glossy, smooth and hairless
• have obvious veins. 

Leaf shape changes depending on the density of infestations.

In open water or on the open-water edge of large infestations leaves are:

• round up to 30 cm in diameter
• curved upwards with wavy edges
• on hollow vase-shaped floating leaf stalks up to 50 cm long. 

In dense crowded infestations leaves are:

• narrower and upright 
• up to 60 cm long (including the stalk)
• on thin stalks.

Flowers are:

• light bluish-purple or dark blue with six distinct petals (the upper petal is darker purple with a yellow mark in the centre)
• 4-7 cm long and 4-6 cm wide
• funnel-shaped 
• on upright stems with between 3 and 35 (but usually 8) flowers on each spike
• produced from mid to late summer and only open for one or two days before withering. 

Fruit are:

• a capsule containing up to 300 seeds
• 10-15 mm long.

When all the flowers on a flower stem have withered, the stem bends into the water. The fruit capsule then matures under water. 

Seeds are:

• 1 to 1.5 mm long 
• roughly egg-shaped with ridges from end to end
• viable for up to 20 years.

Stems:

There are two types of stems:

• erect stems up to 60 cm long, with flowers,
• horizontal vegetative stems (stolons) 10 cm long, which produce new daughter plants.

Roots are:

• fibrous and featherlike 
• black to purple
• up to 1 m long in deep water, trailing below the plant
• anchored in mud or sediment in shallow water. 

Similar looking plants

Water hyacinth is closely related to anchored water hyacinth (Eichhornia azurea). Anchored water hyacinth does not have thick, vase-shaped leaf stalks and its flower petals have serrated edges.

Where is it found?

Water hyacinth grows along the NSW coast from the Queensland border to Kiama in the South East region. The Macleay, Clarence and Richmond catchments have the worst infestations on the North Coast. Large infestations were present in the Hawkesbury River in Greater Sydney during the 1990s. Small remaining populations are still being controlled.

In the North West region, water hyacinth was identified near the Gingham Watercourse near Moree in 1955. By 1976 it had become a major infestation covering 7000 ha. Despite control efforts, a significant seed bank still remains across the region. It has since moved further west, threatening the Murray-Darling system.

Water hyacinth is native to the Amazon basin in South America. It grows on every continent except Antarctica. It was brought to Australia in the 1890s as an ornamental plant. The first record of water hyacinth in NSW was in 1895. By the early 1900s, it had spread along the east coast of Queensland and the north-eastern regions of NSW. In the early 1900s infestations in NSW's northern coastal rivers impeded river navigation.

What type of environment does it grow in?

Water hyacinth grows in tropical, subtropical and warm temperate climates. It grows best in still or slow-flowing fresh water with high nutrient levels. The ideal temperature range is 28-30°C, though it still grows well between 22 and 35°C. It stops growing when the temperature is below 10°C. Although it can tolerate mild frosts, severe frosts will kill the plant. It prefers water with a pH of 7 but tolerates a range of 4 to 8. It is very sensitive to salt water. 

Maps and records

• Recorded presence of Water hyacinth during property inspections (Map: Biosecurity Information System - Weeds, 2017-2024)
  These records are made by authorised officers during property inspections under the Biosecurity Act 2015. Officers record the presence of priority weeds in their council area and provide this to the NSW Department of Primary Industries. Records reflect the presence of the weed on the date of inspection.
  
  

How does it spread?

By seed

The seeds are released from the capsule underwater. Each capsule has between 40 and 300 seeds. The seeds either sink or accumulate in the floating plant mat.  Seed remains viable for up to 20 years in mud or soil. Seeds can be moved to new locations by water flows or via mud stuck to birds, machinery and footwear. 

By plant parts

Water hyacinth infestations increase most rapidly by producing new daughter plants. Each plant can produce 2-4 daughter plants. Most of these are produced in spring to summer. During high water flows and flooding, plant masses can break up and move to new locations.

Plants are also spread by people:

• planting water hyacinth in ponds or dams
• dumping unwanted aquarium plants into waterways
• moving contaminated fishing equipment, watercraft and boat trailers.

References

Australian Water Resources Council (1988). Australian water weeds: general facts, Australian Water Resources Council, Canberra.

Burton, J. (2005) Water hyacinth Eichhornia crassipes. Agfact. P7.6.43 third edition. NSW DPI.

Julien, M.H. & Griffiths, M.W. (1998), Biological Control of Weeds: A World Catalogue of Agents and their Target Weeds. 4th edn, CABI Publishing, Wallingford.

Julien, M.H., Griffiths, M.W. & Wright, A.D. (1999). Biological control of water hyacinth: the weevils Neochetina bruchi and N. eichhorniae: biologies, host ranges, and rearing, releasing and monitoring techniques for biological control of Eichhornia crassipes, The Australian Centre for International Agricultural Research, Canberra.

Parsons, W.T., & Cuthbertson, E. G. (2001). Noxious weeds of Australia. CSIRO publishing.

Queensland NRM (2001). Water hyacinth – Eichhornia crassipes, NRM facts, Queensland Department of Natural Resources and Mines, Brisbane.

Sainty, G.R. & Jacobs, S.W.L. (1981). Waterplants of New South Wales, Water Resources Commission, Sydney.

Wright, A.D. & Purcell, M.F. (1995). Echhornia crassipes (Mart) Solms-Laubach. In  R.H. Groves, R.C.H. Shepherd, & R.G. Richardson. The biology of Australian weeds, vol. 1. R.G. and F.J. Richardson, Melbourne.

More information

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Control

Successful weed control relies on follow up after the initial efforts. This means regularly looking for any new plants or plant fragments and controlling them. Using a combination of control methods is usually more successful.

To tackle water hyacinth:

• Act to control new infestations as soon as possible, ideally before it flowers and sets seed. 
• Treat large, established infestations each year.

Early detection

Control any new infestations as soon as possible.

Physical removal

Remove plants before flowering and seed set. A mass of water hyacinth removed from the water can take up to 12 months to break down. Contact your local council for advice on how to dispose of this weed.

By hand

Hand weeding is effective on small infestations, as long as the rate of removal can stay ahead of the growth of the plants. Take the plants out of the water and leave them somewhere to dry out. Manual removal is unlikely to be effective on large infestations. 

By machine

Mechanical removal can be effective but is expensive. It takes between 600 and 900 hours to harvest one hectare of dense water hyacinth.  

If water hyacinth has washed onto land in flooding:

• use earthmoving equipment to remove it from roads and verges
• windrow into heaps or spread and mulch the plant material to speed up decomposition.

Biological control

Four insects from South America have been released in Australia for water hyacinth control. They are: 

• two weevils Neochetina eichhorniae and Neochetina bruchi and
• two moths Niphograpta albiguttalis and Xubida infusellus.

They have established across NSW but biological controls alone do not control water hyacinth. They reduce flowering and occasionally cause the plant mats to sink. 

Niphograpta albiguttalis has established in northern NSW and Queensland. The larvae of both moth species tunnel into the leaf stalks and buds. Both moths are very damaging to young plants and luxuriant weed growth but their impacts are often temporary and patchy.

In tropical areas of Australia Neochetina eichhorniae has destroyed large infestations of water hyacinth. The adult is grey or black, 4-5 mm long. Adults feed on the young leaves and upper parts of the stalk. They lay their eggs in the thick, vase-shaped leaf stalks. Larvae tunnel through the plant tissue which eventually becomes waterlogged and can die. These weevils are inactive during winter.

Neochetina bruchi looks similar to N. eichhorniae but is slightly larger and a lighter brown colour. It damages the plant in a similar way to N. eichorniae but is more active through the winter. It is well established from northern Queensland to Sydney.

The weevils are still being reared and released in NSW. Contact your local council weeds officer, if you would like more information about biological control for water hyacinth.

Cultural control

Minimise nutrient run-off into infested waterways. Draining or lowering water levels can reduce the area of water hyacinth. Seeds remain viable and will germinate when the area refills with water.

Retaining salty water or naturally introducing it to infested waterways suppresses water hyacinth.

Chemical control

Water hyacinth is usually treated with handgun power sprays from a boat or the bank. Some large infestations have been aerially sprayed. 

Treatments with herbicides should be carried out early in the growing season (generally in spring).

Spraying large entire infestation will cause the weed mat to sink. It then rots, which can de-oxygenate the water and kill fish. To avoid this on large infestations remove as much water hyacinth as possible manually and spray one third of the infestation at a time.

Herbicide options

See Using herbicides for more information.

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PERMIT 92971 Expires 31/03/2028
Metsulfuron-methyl 600 g/kg (LYNX WG herbicide)
Rate: 10 g / 100 L water (add wetter at 200 mL per 100 L)
Comments: Only for enclosed water bodies. Areas within 400 m of potable water supply uptakes are excluded. ONLY apply as a foliar spot spray during non-frost periods using a high volume sprayer/knapsack fitted with calibrated spray equipment. Apply a maximum of 3 applications per year at minimum intervals of 90 days. WARNING: Very toxic to aquatic plants and algae. See permit for more restraints and critical use comments.
Withholding period: A nil withholding period is applicable. However, it is recommended not to graze treated areas for 3 days to ensure product efficacy.
Herbicide group: 2 (previously group B), Inhibition of acetolactate and/or acetohydroxyacid synthase (ALS, AHAS inhibitors)
Resistance risk: High

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2,4-D 300 g/L (Affray 300®)
Rate: 1.0 L in 200 L of water
Comments: Avoid causing submersion of sprayed plants.
Withholding period: Do not graze or cut for stock food for 7 days after application.
Herbicide group: 4 (previously group I), Disruptors of plant cell growth (Auxin mimics)
Resistance risk: Moderate

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Amitrole 250 g/L (Amitrole T® )
Rate: 280 mL to 100 L of water
Comments: Apply prior to flowering.
Withholding period: Nil except check for label for orchards and vines.
Herbicide group: 34 (previously group Q), Inhibition of lycopene cyclase
Resistance risk: Moderate

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Diquat 200 g/L (Reglone®)
Rate: 400 mL /ha plus 150 mL Agral / 100 L water
Comments: Small areas: spray to wet weeds thoroughly. About 1 mL of product should be sufficient to treat 1 square metre of weeds. See label for more comments.
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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Diquat 200 g/L (Reglone®)
Rate: 5.0 to 10.0 L/ha
Comments: Apply as overall spray wetting foliage thoroughly. Use higher rates for heavy infestations or for deep or dirty water. Oxygen depletion of decaying weeds may occur therefore do not spray more than a quarter of the area at any one time
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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Glyphosate 360 g/L (Only products registered for aquatic use)
Rate: 1.0–1.3 L in 100 L of water
Comments: Apply when actively growing, at or beyond the early bloom stage. Use higher rate on dense infestations.
Withholding period: Nil.
Herbicide group: 9 (previously group M), Inhibition of 5-enolpyruvyl shikimate-3 phosphate synthase (EPSP inhibition)
Resistance risk: Moderate

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Glyphosate 360 g/L (Only products registered for aquatic use)
Rate: 6.0–9.0 L/ha
Comments: Apply when actively growing, at or beyond the early bloom stage. Use higher rate on dense infestations.
Withholding period: Nil.
Herbicide group: 9 (previously group M), Inhibition of 5-enolpyruvyl shikimate-3 phosphate synthase (EPSP inhibition)
Resistance risk: Moderate

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Biosecurity duty

The content provided here is for information purposes only and is taken from the 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.
All of NSW	Prohibition on certain dealings Must not be imported into the state, sold, bartered, exchanged or offered for sale.
All of NSW The Water Hyacinth Biosecurity Zone applies to all land within the State, except for the following regions: Greater Sydney or North Coast, North West (but only the local government area of Moree Plains), Hunter (but only in the local government areas of City of Cessnock, City of Lake Macquarie, MidCoast, City of Maitland, City of Newcastle or Port Stephens), South East (but only in the local government areas of Eurobodalla, Kiama, City of Shellharbour, City of Shoalhaven or City of Wollongong).	Biosecurity Zone Within the Biosecurity Zone this weed must be eradicated where practicable, or as much of the weed destroyed as practicable, and any remaining weed suppressed. The local control authority must be notified of any new infestations of this weed within the Biosecurity Zone
Greater Sydney	Regional Recommended Measure* (for Regional Priority - Asset Protection) Land managers should mitigate the risk of the plant being introduced to their land. Land managers should mitigate spread of the plant from their land. A person should not buy, sell, move, carry or release the plant into the environment.
Hunter A Water Hyacinth Biosecurity Zone, is established for all land within the Hunter Local Land Services region except land in the following local government areas: Cessnock Local Government Area, Lake Macquarie Local Government Area, MidCoast Local Government Area, Maitland Local Government Area, Newcastle Local Government Area, Port Stephens Local Government Area.	Regional Recommended Measure* (for Regional Priority - Containment) Entire Hunter Local Land Services region: A person must not, import into the State or sell. Within the biosecurity zone: If the weed is part of a new infestation of the weed on the land, notify the local control authority for the land as soon as practicable. Eradicate the weed or, if that is not practicable, destroy as much of the weed as is practicable and suppress the spread of any remaining weed. Outside the biosecurity zone: Land managers should mitigate spread of the plant from their land. Land managers should reduce the impact of the plant on assets of high economic, environmental and/or social value.
North West An exclusion zone is established for all lands in the region, except the core infestation area comprising the Moree Plains Shire council	Regional Recommended Measure* (for Regional Priority - Containment) Whole of region: Land managers mitigate the risk of new weeds being introduced to their land. Within exclusion zone: Land managers should eradicate the plant from the land and keep the land free of the plant. A person should not deal with the plant, where dealings include but are not limited to buying, selling, growing, moving, carrying or releasing the plant. Notify local control authority if found. Within core infestation: Land managers should mitigate spread of the plant from their land. A person should not buy, sell, move, carry or release the plant into the environment. Land managers should reduce the impact of the plant on assets of high economic, environmental and/or social value.
	*To see the Regional Strategic Weeds Management Plans containing demonstrated outcomes that fulfil the general biosecurity duty for this weed click here

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Reviewed 2024