Why are Nutrients a Problem in Perth?

Nitrogen and phosphorus are two nutrients that naturally occur in aquatic systems. However, when excess nutrients are released into aquatic systems either naturally or anthropogenically, it can cause problems such as eutrophication(nutrient enrichment) which can have devastating effects on ecosystems.

The design on the Perth Metropolitan Area (PMA) has resulted in urban infrastructure such as housing, farming, parks and sports grounds being located close to major water ways such as the Swan-Canning River1and local wetlands. As a result, human actions such as land clearing, sewage and urban runoff, and incorrect disposal of detergents and soaps can increase nutrients in local systems.

1. River Science. Algal blooms in the Swan-Canning estuary: Patterns, causes and history [document on the Internet]. Government of Western Australia; 2005. Available from:

What are the Causes of Excess Nutrients in Our Waterways?

Since European settlement, humans have altered the natural landscape. The clearing of land for agriculture and urban development has modified water movement patterns and reduced the amount of vegetation around water bodies that can utilise nutrients. The addition of excess nutrients from human sources such as sewage, urban runoff and incorrect disposal of detergents and soaps further increase nutrients in our waterways (1). It is therefore critically important to manage the direct and indirect inputs of nutrients into our local rivers, estuaries and wetlands to minimize the impacts to our unique biodiversity in Perth.

1. River Science. Sources of nutrients to the Swan and Canning rivers [ document on the Internet]. Government of Western Australia, 2000. Available from:

What are the Impacts of Excess Nutrients?

A significant increase in inputs of phosphorus and nitrogen into waterways can lead to a toxic algal bloom, also known as eutrophication (Figure 1). This algal bloom can decrease light penetration, oxygen availability and eventually lead to deaths of fish and other aquatic species within the waterbody, which can have significant impacts of the fishing industry. Furthermore, the algal bloom will discolour the waterbody and may give off an unattractive odour, reducing the aesthetic value of the lake and possibly impacting tourism.

Figure 1: Effects of nutrient enrichment in Perth waterways (Source: Jane Chambers)

What causes Phytophthora cinnamomi to spread in the Perth Metro Area?

Locals walking through bush reserves, or recreational activities such as off-roading and BMX bike riding increase the spread of the disease within the PMA, therefore, management has to focus heavily on reducing the human footprint in local reserves, and educating the public about steps they can take to minimise the risk of introducing dieback into their local reserve.

Is Dieback the only disease that affects biodiversity in Perth?

Absolutely not. Many plant pathogens occur naturally in Western Australia, and others are introduced. Some other pathogens that affect biodiversity in Perth include, but are not limited to Uromycladiumtepperianum(rusts),Pucciniapsidii(Myrtle rust), Armillaria luteobubalina(Honey Fungus), Canker disease, Mundulla Yellows, andSphaeropsissapinea(Sphaeropsisblight). For further information on these diseases check out the Department of Primary Industries and Regional Developments Native Plant Diseases.

Which native plants are susceptible to Dieback?

Many plant pathogens occur Phytophthoracinnamomiaffects more than 40% of all native plant species. The Centre for Phytophthora Science and Management (CPSM) have created a list of Western Australian Natives Susceptible to Phytophthora cinnamomi. Additionally CPSM have also produced a list of Western Australian Natives Resistant to Phytophthora cinnamomi.

Dieback can also be an issue in nurseries and gardens. For information on native garden plants that are resistant to dieback click here. For information about how to manage dieback in nurseries click here.



Private Land Owners

Reducing fertiliser use or switching to alternate fertilisers that have a less of an impact on local waterways is a great way for the individual to help reduce excess nutrients in Perth waterways. For information about how to reduce fertiliser usage, alternate fertilisers and other ways to reduce nutrient run-off from the home click here

If you are a private landowner the Department of Biodiversity, Conservation and Attractions have a Healthy Wetland Habitats which can help landholders to develop a wetland management plan to protect and care for the wetlands.

Community Groups / Land Managers

Community members and land manager can locate wetlands and their associated status (Conservation, Multiple Use etc.) through accessing Landgate’spublic map viewer and selecting the layer Geomorphic Wetlands, Swan Coastal Plain (DBCA-019).

Local Councils

Local councils can locate wetlands and their associated status (Conservation, Multiple Use etc.) through accessing Landgate’spublic map viewer and selecting the layer Geomorphic Wetlands, Swan Coastal Plain (DBCA-019). For information on how to manage local wetlands and waterways click here.

Some councils have worked with the Swan River Trust to develop Water Quality Improvement Plans (WQIP) to assist local councils and communities in improving water quality in local areas, these are listed below.

Water Quality Improvement Plans have also been developed for larger estuarine systems in Western Australia, including theSwan-Canning Water Improvement Plan. To find out more information about Water Quality Improvement Plans click here.

Effective management of fertiliser and turf in local reserves is also an important management practice for local councils to prevent nutrient run-off into local wetlands and waterways. For information about the establishment and management of turf grass areas click here.

Department of Water and Environmental Regulation

The Department of Water and Environmental Regulation have great resources on water management and monitoring to reduce excess nutrients in Perth waterways. These resources include Sources of Nutrients to the Swan and Canning Rivers, Guidelines for Nutrient and Irrigation Management Plans, Water Quality Monitoring Program Design, and Field Sampling Guidelines for Surface Water Monitoring.