What are invasive species?

An invasive species is a species occurring as a result of human activities beyond its natural range. The species threatens valued environmental, agricultural, cultural or other social resources by the damage it causes. This can include organisms endemic to a country other than Australia or a native species moved to a new location.

The problem for waterways

Invasive species in waterways and along riparian land are an increasing threat to the health of rivers, estuaries and wetlands in Victoria. The establishment and spread of invasive species is often a symptom of broader land use change and disturbance. Compared to most land, waterways (including riparian land) appear to be especially vulnerable to invasive species. Riparian land is prone to invasion due to high productivity and frequent disturbances. The spread of invasive species through waterways and riparian land is assisted by high connectivity as a result of water flowing downstream, or laterally to the floodplain and associated wetlands. It is common for significant movement of invasive species to occur during flood events.

Invasive species affect waterway conditions and also have the potential to threaten environmental, social, cultural and economic values. Environmental impacts may include predation on, or competition with, native species, loss of habitat and changes to water quality or sediment, nutrient levels and the transmission of disease.

The impacts associated with invasive species are often underestimated as there may be a time lag between their introduction and their effects being noticed, or it may be difficult to calculate the costs associated with the damage caused.

Some invasive species can pose a risk to environmental values, but at the same time support social and economic values, such as recreational fishing. A balanced management approach is therefore required to reduce the impacts of invasive species that cause substantial harm, while continuing to acknowledge that in some limited cases invasive species may provide other benefits that are valued by the community.

Managing invasive species in Victorian waterways

Management of invasive species is complex and requires a high degree of cooperation between international, national, state and regional agencies. The Victorian Government’s Environmental Partnerships and the Invasive Plants and Animals Policy Framework provide the overarching strategic approach for managing invasive species across the whole of Victoria. The Victorian Waterway Management Strategy (PDF, 4.2 MB) sets out the policy direction for issues affecting waterway health, including the threat from invasive species.

The management of invasive species in waterways needs to be holistic and integrated with other waterway management activities, other pest plant and animal control work, and fisheries management activities. It is difficult to eradicate invasive species and therefore management activities to prevent their establishment are critical. To date, management has focused mainly on established invasive species rather than minimising the risk of new species invasions or rapid response to new incursions and/or containment.

It is often impossible to eradicate invasive species in waterways; therefore, management activities to prevent their introduction and establishment are critical. Prevention provides a higher return for investment than eradication, containment or managing their impacts across widespread areas. Coordinated action across Victorian government agencies and working with the community is necessary to integrate environmental programs and achieve multiple outcomes for land, water and biodiversity.

Victoria is a signatory to the National Environmental Biosecurity Response Agreement (NEBRA). The NEBRA sets out emergency response arrangements, including cost-sharing arrangements, for responding to biosecurity incidents that primarily impact the environment and/or social amenity and where the response is for the public good.  A national biosecurity incident response under NEBRA would be considered for new incursions of invasive species in waterways if such incursions were assessed as being of national significance and  the invasive species was likely to be eradicable.


This project assessed the risk of spread of selected high priority freshwater aquatic invasive species through the Victorian water grid, and identified pathways that led to the introduction, establishment, and spread of invasive species in Victoria. Research results were documented in two reports:

Risk of aquatic invasive species spread through the Victorian water grid

Review of high-risk pathways for the spread of invasive species

This research allows informed decisions to be made regarding monitoring and management of invasive species and the pathways leading to their establishment and spread.

This project developed education and awareness raising material about invasive species that affect waterways that specifically target community and industry stakeholders. Engaging with the community and industry is a fundamental component to the framework for management of invasive species in waterways.

Help stop freshwater pests in Victoria's waterways

Wetland managers seek guidance and support regarding which invasive species should be the focus of management effort, and how they can be most effectively managed to minimise their impacts on wetlands.

This project developed:

  • A training course for the management of rabbits, foxes, pigs and carp;
  • Fact sheets outlining the impacts of these four species on wetlands;
  • A process to prioritise 174 wetland weeds currently known from Victorian wetlands; and
  • A collation of information on the impacts of 28 priority wetland weeds.

View these fact sheets, reports and training details on Managing Wetlands.

Exotic species such as willows were historically planted along waterways for erosion control and aesthetic purposes. The spread of these species over time has degraded riparian land. Consequently, over the last 20 years or so, catchment management authorities have been removing willows along many Victorian waterways.

These willow management programs have sometimes caused concern with the public, particularly landholders and recreational fishers, who have a strong interest in the health of our waterways.

Find out more about willow management in Victoria.

Page last updated: 26/01/23