Quick Facts

Quick facts

• Cabomba (Cabomba caroliniana) is a mostly submerged, feathery-leaved aquatic herb that grows quickly and produces vast amounts of submerged plant material.
• It is still sold as an aquarium plant in some States, which makes control very difficult. Its spread has been assisted by the deliberate 'seeding' of waterways to ensure a wild supply for the aquarium trade.
• Weed control in aquatic environments is difficult, and control options are limited by social and environmental considerations.
• Cabomba is sensitive to drying out and requires permanent shallow water. So, where possible, draining a water body can provide temporary control.

What Does It Look Like?

What is it?

Cabomba (Cabomba caroliniana) is a perennial aquatic herb with branched stems that have white or reddish brown hairs growing on them. It is fully submerged, except for occasional leaves and flowers that float and later emerge on stalks several centimetres above the water surface. It roots at the nodes of creeping runners (stolons or rhizomes) and lower stems into the substrate on the bottom of water bodies, and the stems (up to 5 m or even sometimes 10 m long) can reach the surface. Parts of the plant can survive free-floating for 6–8 weeks.

The underwater leaves are arranged in opposite pairs or sometimes in whorls of 3 on the stems. They are circular to kidney-shaped in outline (up to 6 cm wide) and are finely divided into narrow linear segments less than 1 mm wide, which are usually further divided, giving the leaves a feathery fan-like appearance (hence Cabomba being known as Fanwort in some countries). These leaves secrete a sticky mucus or gelatinous slime that covers the submerged parts of the plant. The few (if any) floating leaves are small (up to 2 cm long), not divided, narrowly elliptic or diamond-shaped and borne alternately on the flowering branches. The solitary flowers are about 2 cm wide, and range in colour from white (with a yellow centre) to pale yellow, and may also have a pink to purplish tinge.

The plant description is based on Jacobs (1990), Entwisle (1996), Mackey (1996), Mackey & Swarbrick (1998), Cowie et al. (2000), Parsons & Cuthbertson (2001), CRC (2003), CSIRO Entomology (2004) and Stanley & Orchard (2007) and NRETA (no date).

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

Flower colour

White

Growth form (weed type/habit)

Aquatic, Herb

Where it currently grows? Preferred habitat

Cabomba grows in still or slow-moving freshwater, in ponds, lakes, dams, channels and quiet streams. It is sensitive to drying out and requires permanent shallow water, usually less than 3 m, but up to 10 m, deep. It grows well on a silty bed, but less well on hard surfaces. It grows quickly and so can respond to wide fluctuations in water depth (CRC 2003).

Cabomba grows well in high nutrient environments with a low pH; in more alkaline waters it tends to lose its leaves. High calcium levels also inhibit growth. Unlike other aquatic weeds, Cabomba can grow well in turbid water. It prefers a warm, humid climate with a temperature range of 13–27 ºC but can survive when the surface of the water body is frozen (CRC 2003).

Are there similar species?

Cabomba may be easily confused with other aquatic species, notably the Hornworts (Ceratophyllum species) and some Watermilfoils (Myriophyllum species). The closely related Pink Cabomba (Cabomba furcata) is also sold as an aquarium plant. It is pink in colour with purple flowers and is not considered a weed in Australia (CRC 2003).

NRETA (undated) provides a useful comparison guide between Cabomba and similar species. See http://www.nt.gov.au/nreta/natres/weeds/ntweeds/Cabomba/species.html . Identification should be confirmed by experts.

Why Is It A Weed?

What are its impacts?

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

Cabomba is choking waterways along Australia's east coast (CRC 2003). Cabomba grows quickly and can therefore block slow-moving waterways such as irrigation channels, ponds, dams and lakes (Richardson et al. 2006), significantly reducing storage capacity by siltation (Faithfull & Gunasekera 1999, Land Protection 2006). It also decreases water quality by causing colouring, odours, accumulation of organic matter and stagnation in streams (Ensbey 2000, CRC 2003).

Cabomba is an aggressive invader of native freshwater systems, particularly if they are nutrient rich, excluding native plant species by blocking out sunlight and competing for space and nutrients. It can also have a negative impact on native fish, aquatic invertebrates, birds, reptiles and other animals (CRC 2003, CSIRO Entomology 2004, Land Protection 2006; NRETA undated). At the same time, it can create a suitable habitat for mosquito breeding (NRETA undated).

Dense infestations of Cabomba degrade the aesthetic value of streams (Ensbey 2000) and impede aquatic transport and recreational activities such as swimming, diving and boating (Ensbey 2000, CRC 2003, Land Protection 2006).

How does it spread?

Cabomba does not appear to produce mature, fertile fruit or seed in Australia (CRC 2003, Stanley & Orchard 2007). It reproduces and spreads here by the movement of small plant pieces that readily break off the brittle stems and runners (CRC 2003). Fragments may survive in water for 6-8 weeks, and a detached shoot as short as 10 mm with at least one pair of leaves can grow into a mature plant (CRC 2003). Fragments can be spread by water flow and possibly by attachment to waterfowl, water craft, and boat trailers, also by disposal of unwanted aquarium plants, as well as being deliberately planted to allow wild cultivation for the aquarium trade (Mackey & Swarbrick 1998).

It is still illegally sold as an aquarium plant in many States of Australia, supplied by both growers and wild harvest operations. The trade represents a $300 000-a-year industry, while conservative 1999 estimates place the national cost of Cabomba control at more than $500 000 (CRC 2003).

See NRETA (undated) for further information on the spread of Cabomba.

What is its history in Australia?

Cabomba is widely cultivated as an ornamental for fish ponds and aquaria, and this is how it was probably introduced to Australia. It appears to be a relatively recent introduction, with the earliest herbarium record in 1967 from cultivated material at Oyster Bay in New South Wales (Mackey & Swarbrick 1998). Cabomba was first recognised as naturalised in 1981 (Faithfull & Gunasekera 1999) and there are various reports of it spreading in Queensland from the mid 1980s (see Mackey 1996 and Mackey & Swarbrick 1998).

How To Manage It?

Best practice management

Once established, Cabomba is extremely difficult to control, so prevention is therefore the best means of control. This requires community awareness for early detection and notification of any stands. The spread of Cabomba in Australia has also been aided by the deliberate 'seeding' of waterways to ensure a wild supply for the aquarium trade (CRC 2003). Some strategies to help prevent spread include the following:

• Dispose of Cabomba from aquariums responsibly, e.g., by drying and burning the entire plant.
• Educate people to use other species of aquarium plants
• Local agencies need to be able to close waterways to prevent spread
• Develop protocols for washdown of boats, trailers and fishing equipment before they leave an infested site (CRC 2003).

Physical control: cutting and removal is suited to accessible areas of closed water bodies with established heavy infestations. However, Cabomba grows so quickly that treatment is only likely to maintain a clear water surface for a few weeks and the cost is high. Hand pulling by divers is best suited to isolated plants and small areas (CRC 2003).

The deliberate lowering of the water level (drawdown) may be the best option for drinking water supplies. If the base of the water storage dries out completely there is little chance of Cabomba surviving, but if it remains damp there is a more than 50% chance it will return. Because Cabomba requires direct sunlight, shading has been used to kill it in small areas. However, the cost is prohibitive for large-scale programs. Long-term benefits are expected from maintaining tree coverage along the edges of creeks and rivers to discourage Cabomba establishing in the shallows (CRC 2003).

Chemical control: is difficult because of the problems associated with applying chemicals in water and the potential to affect non-target species. It has also shown some resistance to herbicides (CRC 2003). See the Australian Pesticides and Veterinary Medicines Authority for chemical information at http://www.apvma.gov.au .

Biological control: has not yet been attempted although some research has been conducted (Mackey & Swarbrick 1998, Julien & Schooler 2004). An active biocontrol research program for cabomba (Cabomba caroliniana A. Gray) is currently led by CSIRO Australia and supported by the Rural Research and Development for Profit program in Australia (Harvey et al., 2023).  

For further information see CRC (2003) and the NRETA (undated).

Does it have a biological control agent?

NO

When does it grow? (lifecycle/growth calendar)

In northern Queensland Cabomba grows and flowers continuously. However, in southern areas it flowers and has its maximum growth period in summer. It dies back in winter and lies on the bottom of the water body, where the stems break up and provide dispersal material. New growth starts from these dislodged stem pieces (CRC 2003). See Mackey (1996), Mackey & Swarbrick (1998) and NRETA (undated) for further information.

Where Is It Found?

Which states and territories is it found?

NSW, NT, QLD, VIC

What areas within states and territories is it found?

Cabomba is naturalised in widely scattered locations in northern and eastern Australia (Stanley & Orchard 2007). Most infestations occur in the hinterlands of northern New South Wales and southern Queensland. However, infestations have been recorded as far apart as Darwin and central Victoria (CRC 2003).

In Queensland the heaviest infestations occur in shallow dams on the Sunshine Coast and some reservoirs in the greater Brisbane area (e.g., Lake Kurwongbah), but significant infestations also occur in Far North Queensland (e.g., Atherton Tableland and Cairns region). Cabomba is growing in numerous creeks and river systems on the New South Wales North Coast (e.g., near Murwillumbah) and the Central Coast region, as well as in lakes in central Victoria (e.g., Lake Nagambie and near Foster).

In the Northern Territory, the Marlow Lagoon infestation (Mackey & Swarbrick 1998, CRC 2003, CSIRO Entomology 2004, Stanley & Orchard 2007) has been eradicated, and the only known infestation now is in a section of the Darwin River downstream of Darwin River Dam (NRETA undated).

Cabomba infestations are isolated and currently affect relatively few water bodies. However, based on climate and the availability of water, it could easily spread further across southern and eastern Australia. Waterways from Cape York to Hobart and from Sydney to Perth are at risk. Additionally, Cabomba could potentially infest the Ord River irrigation system (CRC 2003).

Where does it originate?

There are five species of Cabomba, from tropical and warm temperate areas of the Americas (North, Central and South America) and the West Indies (Stanley & Orchard 2007). None is native to Australia.

Cabomba is native to eastern USA, southern Brazil, Paraguay, Uruguay and north-eastern Argentina (Stanley & Orchard 2007). It has been spread throughout the world by the aquarium trade (CRC 2003) and is now naturalised, usually from discarded aquarium plants, in many countries, including Australia and New Guinea (Stanley & Orchard 2007).

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

Cabomba caroliniana

Other scientific names (synonyms)?

Does it have other known common name(s)?

Fanwort, Carolina Watershield, Fish Grass, Washington Grass, Watershield, Carolina Fanwort, Common Cabomba