Pests and invasive species


SoE 2011 provided information on the pressure of invasive species, including cane toads (Rhinella marina, formerly Bufo marinus), common carp (Cyprinus carpio), eastern gambusia (Gambusia holbrooki), goldfish (Carassius auratus) and various Weeds of National Significance. Other invasive species exerting pressure on inland waters include pigs and buffalo, redfin perch (Perca fluviatilis), various tilapia species, oriental weatherloach (Misgurnus anguillicaudatus) and redclaw crayfish (Cherax quadricarinatus).

Cane toads have now spread into the Kimberley and upper reaches of the Fitzroy River in Western Australia (Pusey & Kath 2014), and inland western Queensland, with estimates of expansion of around 10–50 kilometres per year. Expansion in the cane toad range has been found to reflect a shift in the species’ realised niche (i.e. a shift aided by the presence of novel biotic and abiotic conditions in the invaded range), as opposed to the evolutionary shifts in range-limiting traits that affect the range of any species (Tingley et al. 2014).

The challenge of managing feral freshwater fish, and understanding their extent and impact has spawned a national online information resource, called Feral Fish Scan. Feral Fish Scan is taking a crowdsourcing approach to provide a community resource for mapping feral fish, which, over time, will provide further support for management. A heat map of carp extent in Australia shows areas similar to those reported in 2011. Increases have occurred in western South Australia, and central and southern Victoria (Figure WAT8). Detailed local monitoring may provide more accurate assessment of the presence and extent of feral species; for example, the Lake Eyre State of the Basin Committee found no carp in a survey of an area that may have formerly contained carp. There is also some evidence that carp numbers have increased since the 2010–11 flooding of the Murray River (Koehn et al. 2016).


The eastern gambusia is one of the more widespread invasive freshwater fish species in Australia, with sightings in all mainland states and territories (Figure WAT9). They are also known to be present in the Tamar River and nearby constructed water bodies in Tasmania (Coleen Cole, Department of Primary Industries, Parks, Water and Environment [DPIPWE], pers. comm., 10 June 2016). However, data from the Atlas of Living Australia show no significant expansion in eastern gambusia extent since 2011 (DPIPWE, peer review comments).


The problems of invasive ornamental fish have gained the attention of the Senate Environment and Communications References Committee. The committee produced an environmental biosecurity report in 2015 that identified a focus within committee submissions on the threat posed by ornamental fish, noting that ‘of 40 exotic fish species known to have established in Australian waterways, up to 30 were imported as aquarium fish’ (SECRC 2015). The known pressures of invasive fish species include impacts on both native freshwater fish and native frogs. Other pressures, such as on habitat and invertebrate species, are largely unknown.

Two aquatic Weeds of National Significance were added to the list in 2012, as part of an update that added 12 new weeds (Australian Weeds Committee 2012):

  • Sagittaria or arrowhead (Sagittaria platyphylla), an emergent aquatic plant native to the southern areas of North America, was introduced as an ornamental pond plant. Mature plants grow up to 1 metre tall and can produce up to 20,000 seeds, which are mostly dispersed by water.
  • Water hyacinth (Eichhornia crassipes), a free-floating aquatic plant native to South America, was introduced as an ornamental pond plant in the late 1800s. Under favourable conditions, plants can double in size in as little as 8 days, and seeds can remain viable for up to 20 years.

The distribution of these plants is shown in Figures WAT10 and WAT11.

Argent RM (2016). Inland water: Pests and invasive species. In: Australia state of the environment 2016, Australian Government Department of the Environment and Energy, Canberra,, DOI 10.4226/94/58b656cfc28d1