Quick Facts

Quick facts

• Water Hyacinth (Eichhornia crassipes) is a free-floating, aquatic herb distinguished by its broad, glossy green leaves with swollen, spongy leaf stalks, and its showy, blue to mauve flowers with distinctive markings on the petals.
• It is one of the world's worst weeds, being particularly serious in slow-flowing or stagnant freshwater in tropical and subtropical areas.
• It obstructs waterways, reduces fish production, harbours mosquitoes, and severely disrupts life in communities along rivers and lakes
• It is a declared noxious plant in all states and territories and has also been identified as a target for biological control.
• Biological control has been effective in some tropical regions.
• Management requires integrated control programs and monitoring to prevent its further spread.

What Does It Look Like?

What is it?

Water Hyacinth (Eichhornia crassipes) is an erect, free-floating (sometimes attached to the mud and creeping), aquatic perennial herb, varying from 10 cm to 1 m in height where nutrient levels are high. Its roots are black to purple, feathery and up to 1 m long hanging in the water. They are usually short if the water is nutrient-rich. It also has horizontal stems (stolons) which root at the joints (nodes) to form daughter plants.

The leaves radiate from the base to form a cluster or rosette. The leaf stalk (petiole) is spongy, often inflated and buoyant, 2.5-75 cm long, up to 3 cm in diameter. It is short and abruptly swollen in young plants and more tapered and slender in adult plants. The leaf blade is flat, thick, ovate or circular to rounded-oblong, up to 15 cm or sometimes to 25 cm across, with a tip that has an abrupt point or is blunt or rarely indented, glossy green, finely striated with numerous longitudinal veins, the margin gently upcurved and often slightly wavy.

The flowering stalk is up to 50 cm or more long and bears a flower spike that slightly exceeds the leaves. The flower spike is up to 20 cm long, with few to many crowded flowers. The showy flowers are 3-7 cm across with 6 'petals' (actually the lobes of the calyx and the corolla) that are 3-5 cm long, fused below and vary in colour from sky-blue to bluish purple-lavender, lilac-blue, lilac-mauve, pale violet or sometimes white, with the upper lobe having a darker purple or blue patch with a yellow centre.

The fruits are 3-chambered capsules to about 15 mm long, containing up to 300 ribbed seeds about 1-1.5 mm long. The fruiting structure recurves to become submerged (Aston 1973; Sainty & Jacobs 1981; Aston 1987; Stanley & Ross 1989; Cunningham et al.1992; Jacobs 1993; Conn 1994; Wright & Purcell 1995; Parsons & Cuthbertson 2001; Sainty & Associates 2001; Sainty & Jacobs 2003).

For further information and assistance with identification of Water Hyacinth contact the herbarium in your state or territory.

Flower colour

Blue, Purple

Growth form (weed type/habit)

Herb, Aquatic

Where it currently grows? Preferred habitat

Water Hyacinth grows on still or slow-flowing water, in freshwater rivers and other watercourses, lakes, swamps, lagoons on river floodplains, reservoirs and farm dams. It prefers and proliferates in nutrient-rich, subtropical and tropical conditions. It does not thrive or barely survives in fresh clean water such as good-quality tap water (Sainty & Jacobs 1981; Sainty & Associates 2001). Water Hyacinth persists on saturated soils; plants lying in mud grow at a reduced rate (Aston 1973; Sainty & Jacobs 1981). Although it grows most rapidly in warmer areas it will survive a fair degree of cold, including occasional light frosts (Romanowski 1998), but is killed by salt water (Aston 1973).

Are there similar species?

Water Hyacinth is similar to the aquatic weeds Water Lettuce (Pistia stratiotes) and Salvinia (Salvinia molesta) in forming floating obstructive mats, but it is readily distinguished by its showy, pale blue to lavender flowers with a darker purple and yellow blotch, and by having some leaves with a swollen, buoyant base to their leaf stalk.

A related exotic plant is Blue Pickerel Weed (Pontederia cordata), which is often planted as an ornamental around garden water features but is a taller plant rooted in soil at the water's edge. It also has glossy spoon-shaped leaves and tall crowded spikes of smaller mauve or rarely white flowers. The native plant Ornduffia reniformis [as Villarsia reniformis] has glossy, fleshy, kidney-shaped leaves, the back of which is dotted with dark pores. It is usually found in shallow or temporary pools where it is rooted in mud at the water's edge, sending out long runners. Its flowers are yellow with 5 petals. (Southern Tablelands and South Coast Noxious Plants Committee, no date).

The native Monochoria cyanea, from the same family as Water Hyacinth, occurs in north-central New South Wales and northern Australia but it has sprawling, elongated stems, remains anchored to the bottom of water bodies, and does not have the swollen leaf stalks or petal markings found in the later species.

Why Is It A Weed?

What are its impacts?

Water Hyacinth is a Weed of National Significance (WONS). It is regarded as one of the worst weeds in Australia because of its invasiveness, potential for spread, and economic and environmental impacts.

Water Hyacinth is declared as a noxious plant in all states and territories and is on the World Conservation Union's list of the world's 100 worst invasive alien species (ISSG 2000). It is a highly invasive aquatic plant that has become a pest of waterways around the world. It grows aggressively in nutrient-rich stationary or slow-moving freshwater to quickly form dense mats. A single plant has been known to develop in one season into a patch covering about 600 square metres (Aston 1973).

These mats rapidly degrade environments in various ways. They block and choke waterbodies, obstructing water flows in natural watercourses, natural and constructed lakes and ponds, irrigation and flood mitigation channels, and reservoirs and dams. This in turn interferes with and reduces boating, fishing, swimming and other water recreational activities. They can block water pumps, inlets of boat engine water cooling systems and other equipment, and have the potential to interfere with hydro-electric generators. Masses can build-up at bridges, fences and other structures especially during floods, creating a dam and endangering the structure (Sainty & Jacobs 2003).

Infestations reduce water quality as rotting vegetation reduces the oxygen content and fouls the water, impacting on native plants and animals and making water unfit for drinking by humans and livestock. Biodiversity will decline as dense mats reduce light levels, temperature and oxygen in the water below, excluding native aquatic plant species, and altering or destroying natural wetlands and habitat for native invertebrates, amphibians, fish and birds.

Increased loss of water through transpiration (Sainty & Jacobs 1981) has impacts on water storage and supply.

Water Hyacinth infestations can limit access by stock and wildlife to water, and are a potential hazard to young children and livestock if they become entangled in dense vegetation. It can provide shelter for mosquitoes and other disease-spreading organisms (Sainty & Jacobs 2003). Dense mats may be colonised by other plant species and greatly accelerate freshwater succession (Weber 2003), aging a wetland.

Some of the uses of Water Hyacinth are described by Saint & Jacobs (1981) and Parsons & Cuthbertson (2001).

How does it spread?

Water Hyacinth spreads vegetatively by stolons rooting at nodes to produce new plants, eventually developing into mats covering large areas (Sainty & Jacobs 1981). Vegetative propagation is most rapid in nutrient-rich water. Stolons can be broken off and drift in water, aided by wind, currents and floods, to form new colonies. Infestations can also break up into 'rafts' that drift wherever winds and currents take them and so a whole river system can be infested (Parsons & Cuthbertson 2001).

Seeds are dispersed by water and may germinate within days or remain dormant in mud for possibly 15 or more years. Seeds and stolons are also dispersed by birds, movement of mud and sediments, contaminated boats and boating equipment, and in discarded pond refuse (Muyt 2001; Parsons & Cuthbertson 2001).

What is its history in Australia?

Water Hyacinth was deliberately introduced into Australia as an ornamental plant for garden ponds, but was subsequently discarded into waterways or even deliberately planted in lakes and watercourses (Cowie et al. 2000). It was first recorded from Queensland and New South Wales 1894-1895. By the early 1900s it had spread, and was recognised as a weed with pest potential, along the east coast of Queensland and north-eastern New South Wales (Aston 1973; Harley 1981; Stanley & Ross 1989). In the Northern Territory it was found at Fogg Dam near Darwin in the 1970s and a few plants were located on the Magela Creek floodplain in September 1983 (Cowie et al. 2000). In South Australia, Water Hyacinth was formerly found in quantity on the Murray River, but was eradicated by 1954 (Jessop 1986). In central-south Victoria, populations have been eradicated or are controlled by current management procedures (Conn 1994). In Western Australia, dumped aquarium material spread to cover Lake Monger near Perth in 1947 and was soon eradicated, but Water Hyacinth has since invaded other freshwater lakes and swamps in the Perth region (Hussey et al. 1997).

How To Manage It?

Best practice management

Water Hyacinth is declared as a noxious plant in all states and territories. It has also been recognised as a target for biological control through a cross-jurisdictional government process. This allows activities to be undertaken to develop effective biological controls. 

Water Hyacinth can be extremely costly to control once infestations are allowed to spread so preventing its spread into uninfested areas is vital. Reduce nutrient levels entering waterbodies to lower the risk of invasion and spread (Muyt 2001). It should not be cultivated or grown in garden ponds (Sainty & Jacobs 2003) and pond material must not be discarded into waterbodies

Non-chemical control: Small infestations can be removed by hand. Harvester machines are required for clearing larger areas (Weber 2003). The weight of plant material can be enormous, making physical removal only appropriate where suitable equipment is available or infestations are easily accessible (Muyt 2001). Removed material must be disposed of properly, such as drying and burning (Land Protection 2007).

Chemical control: There are several herbicides effective on Water Hyacinth and these need to be approved for use in aquatic environments. Contact your local council or weed control authority for advice on weed control. Also see the Australian Pesticides and Veterinary Medicines Authority (APVMA) for chemical information http://www.apvma.gov.au 

Follow-up programs and monitoring will be required after physical removal or chemical control due to the likelihood of regeneration from seed which can survive in mud and sediments for many years. Waterbodies such as farm dams can be drained to kill existing plants, but plants are likely to grow from the stored seed bank so ongoing monitoring and treatments will be required.

Biological control:  It has been effective in some tropical regions (Sainty & Associates 2001), but with little or no impact in cooler climates (Muyt 2001). Information on biocontrol is provided by Forno & Wright (1981), Harley (1981), Waterhouse (1994), Wright & Purcell (1995), Parsons & Cuthbertson (2001), Center et al. (2002), Burton (2005), CSIRO Entomology (2005, no date), Kathiresan (2005) and Land Protection (2007).

Control is best through a combination of habitat manipulation (denying the plant water may be possible in some situations), biological control agents and approved herbicides (Sainty & Jacobs 2003). Mechanical removal of dead plants will help avoid water quality degradation by masses of rotting plants (Plant Protection 2007). Integrated control programs, including continued monitoring, will control and prevent the further spread of Water Hyacinth (Wright & Purcell 1995; Muyt 2001; Parsons & Cuthbertson 2001; Burton 2005; Land Protection 2007).

Does it have a biological control agent?

YES. Four agents: leaf feeding weevils (Neochetina eichhorniae, Neochetina bruchi) and two stem-boring moths (Niphograpta albiguttalis and Xubida infusella). Ongoing mass rearing and repeated releases of the two weevils and post release monitoring by University of Wollongong (Harvey, et al 2023).

When does it grow? (lifecycle/growth calendar)

Flowering of Water Hyacinth occurs in summer and sometimes into autumn (but can begin as early as October), with each flower opening for 1-2 days and then withering. After a spike has finished flowering, the stalk gradually bends down into the water to submerge the developing fruit, which contains numerous seeds. After 2-3 weeks the seeds are released, drop to the bottom and sink into the mud where some germinate the following spring, and the seedlings float to the water surface to develop into new plants. Much germination occurs on mud beside waterbodies or on bottom mud after water has been drained. Seeds can germinate in a few days or remain dormant for possibly up to 15 years. The top growth usually dies back in autumn, but the crowns of the plants overwinter and begin new growth the following spring (Aston 1973; Sainty & Jacobs 1981; Cunningham et al. 1992; Wright & Purcell 1995; Williamson & Faithfull 1998; Muyt 2001; Parsons & Cuthbertson 2001).

Where Is It Found?

Which states and territories is it found?

NSW, NT, QLD, VIC, WA

What areas within states and territories is it found?

Water Hyacinth is most common in coastal areas of eastern Australia from southern Cape York Peninsula, Queensland, to near Kiama, New South Wales. Other significant occurrences are on the Mitchell River on western Cape York Peninsula, near Mount Isa and Georgetown in Queensland, near Darwin in the Northern Territory, and on the Gwydir River system near Moree, New South Wales (Harley 1981; Aston 1987). It has also been recorded from Western Australia (near Perth), South Australia (although it is uncertain whether it has naturalised here), Victoria and southern New South Wales, where infestations have since been eradicated or are controlled.

Where does it originate?

Water Hyacinth is native to the Amazon Basin in South America, but is now introduced and widespread as an aquatic weed throughout warm freshwaters of the world. It was spread from the late 1800s as an attractive ornamental plant for water features. It mainly occurs in tropical to temperate climatic zones to latitudes around 40 degrees (Aston 1973; Sainty & Jacobs 1981; Cronk & Fennessy 2001; Weber 2003).

National And State Weed Listings

Is it a Weed of National Significance (WONS)?

YES

Where is it a declared weed?

Declared in all states and territories

Government weed strategies and lists – Weeds Australia

Is it on the National Alert List for Environmental Weeds?

NO

Government weed strategies and lists – Weeds Australia

Is it on the Agricultural Sleeper List?

NO

Government weed strategies and lists – Weeds Australia

Names And Taxonomy

Main scientific name

Eichhornia crassipes

Other scientific names (synonyms)?

• Eichhornia speciosa Kunth,
• Pontederia crassipes Mart.

Does it have other known common name(s)?

Water Orchid, Nile Lily