Cabomba

(Also known as Fanwort)

Cabomba caroliniana

Family: Cabombaceae

Type of weed:

Flowering Months: , ,

Description

A completely submerged aquatic plant except for its flowers and occasional floating leaves. The roots attach to the bottom of the water body and stems can be up to 10m long, but usually range up to 5 m.

Submerged leaves and stems have a thin gelatinous coating. Leaves are arranged in opposite pairs along the stems and are finely dissected giving the characteristic feathery, fan-shaped appearance.

Flowers are single, milk-white, pale yellow or purplish, approximately 2 cm in diameter and appear mainly in summer. Flowers emerge from the water during the day and recede into the water overnight. The raised flowers are often the first visible sign of an infestation.

Note:

The genus Cabomba consists of five recognised species: C. aquatica, C. caroliniana, C. furcata, C. haynesii and C. palaeformis. C. caroliniana is the only species known to have become naturalised in Australia. The current definition of C. caroliniana includes the previously separate species C. australis and C. pulcherrima, as well as several natural and horticultural varieties.

Cabomba occurs in several locations in NSW. The most severe infestations are on the NSW far north coast in the upper catchments of the Richmond River and the Burringbar Creek system. These infestations have existed for about 10 years.

Treated infestations include Glenbrook Lagoon in the Blue Mountains in 2014.

Cabomba has a much broader potential distribution, and most waterways throughout eastern, central and southern NSW could be at risk of invasion by Cabomba.

Cabomba will invade freshwater systems, particularly if they are nutrient rich, slow-moving, or permanently standing water less than 4 m deep. Dams, ponds, lakes and freshwater streams all provide habitat for Cabomba, as well as the margins of deeper water bodies or faster moving waterways. It prefers fine, soft silty sediments and is less vigorous on stony, clay or sand substrates.

Cabomba prefers warm-temperate, humid climates with rainfall throughout the year. Light availability is the main environmental variable affecting Cabomba growth, although it can tolerate very low light intensities.

Dispersal

Stems break easily when disturbed, creating small fragments that float on the water surface and can spread throughout a catchment by normal flows or flooding. Cabomba reproduces from these small fragments, which can be moved between catchments and waterbodies through fishing activities and equipment, watercraft and trailers, and animals.

Impact on bushland

Cabomba grows quickly and produces vast amounts of submerged plant material. The monoculture that results from fast-growing submerged Cabomba infestations excludes native aquatic plants and alters the aquatic environment for other organisms. Biodiversity is reduced as a result. Where large masses of Cabomba are growing the accumulation of dead and dying material lowers dissolved oxygen levels.

Cabomba is regarded as a major threat to freshwater systems due to its range of environmental, social and economic impacts.

Dense stands of cabomba cause many problems including:

  • swimming hazards and public safety concerns as drowning is a risk for entangled swimmers;
  • restriction of navigation and recreational use of water bodies;
  • degradation of water quality resulting in foul-smelling, stagnant, oxygen deficient water;
  • degradation of aesthetic values as water surfaces become dark, still and stagnant;
  • displacement of native aquatic plants and animals and alteration of aquatic habitats reducing biodiversity;
  • contamination and discoloration of potable water increasing costs of treatment and storage;
  • blockage of pumps, reduced pumping efficiencies and increased running costs.

Distribution

Alternative planting

Native plants

Council provides a tool, on its Mountain Landscapes website, to help you choose native alternative plantings. Choose your village, soil, vegetation community and the purpose of your planting, and the tool will give you suggestions.

There are native nurseries in several Blue Mountains villages, including Glenbrook, Lawson and Katoomba. Please also ask at your favourite local nursery.

Control

Early detection is critical because once Cabomba is established it is extremely difficult to control.

If you see Cabomba do not attempt to control it. Please immediately contact Council’s Noxious Weeds Team or Council’s Aquatic Systems Team on 4780 5000.

For more info

For key points on these techniques: