22 February 2020

Algal bloom update #5 - extension to Middle Swan

The Department of Health’s algal bloom warning for the Swan and Canning river systems remains in place and continues to extend into the upper reaches of the Swan.

Over the last month the toxic Alexandrium bloom has increased in concentration and is now impacting waterways as far upstream as Middle Swan (Reid Highway) Bridge, Middle Swan.

Fish, crabs or shellfish collected from within the following waterways should not be consumed due to the higher recent Alexandrium algae concentrations and the potential for increased toxin levels:

  • the Swan River – from Pelican Point, Crawley to the South of Perth Yacht Club, Applecross and upstream to Middle Swan (Reid Highway) Bridge, Middle Swan (this includes the commonly known areas of Como Jetty, Matilda Bay, Perth Waters, Elizabeth Quay, Barrack Street Jetty, Claisebrook Cove, Maylands Yacht Club, Ascot Waters, Hind Reserve, Riverside Gardens, Garvey Park, Sandy Beach Reserve, Point Reserve, Kings Meadow,Fish Market Reserve and Woodbridge Riverside Park)
  • the Canning River – from the South of Perth Yacht Club and upstream to Kent Street Weir (this includes commonly known areas of Canning Bridge, Mt Henry Bridge, Salter Point, Shelley Bridge, Riverton Bridge, and Castledare).

The algal bloom warning area covers a large area, but has buffer zones built in as a precaution.

Toxin testing in December and mid-January confirmed that some mussel samples collected in the affected area exceeded the comparable food safety guideline level.

Crabs tested did not exceed this level but higher Alexandrium concentrations in both the Swan and Canning rivers over the last month are likely to result in increasing toxin levels.

Additional testing is underway to better determine how this alga affects fish, crabs and shellfish.      

The ingestion of toxins produced by this microscopic species of algae can produce a type of poisoning known as paralytic shellfish poisoning (PSP). Cooking does not destroy these toxins.

People who consume wild shellfish, crabs or fish collected from the affected area of the Swan or Canning rivers may experience symptoms including:

  • tingling or numbness of the lips
  • prickliness of the fingertips and toes
  • nausea or vomiting
  • impaired balance
  • dizziness
  • slurred speech
  • double vision
  • weakness
  • difficulty in swallowing or breathing
  • loss of fluids and diarrhoea.

In severe cases PSP may cause muscular paralysis in people who consume affected shellfish, crabs or fish. Shellfish includes oysters, mussels, clams, pipis, scallops, cockles and razor clams.

Anyone who has consumed shellfish, crabs or fish collected from the affected area of the Swan or Canning rivers and experiences any of these symptoms should seek urgent medical attention, particularly if they have difficulty breathing.

They should also retain uneaten portions of mussels, crabs or fish to help determine a likely cause of any symptoms.

As a general rule people should avoid eating recreationally collected shellfish in rivers, estuaries or other waterways where there is an increased likelihood of contaminant or nutrient inputs that may result in chemical, algal toxin and/or pathogen uptake.

Farmed shellfish purchased in supermarkets and other commercial outlets in WA are not affected because there is a strict quality assurance program to ensure they are safe for human consumption.

Other recreational activities including swimming, skiing and boating are not affected by this microalgae species, but as a general rule swimming should be avoided in areas of discoloured water.

Health warning signs advising against crabbing, shellfish collection and fishing have been erected at key locations including bridges, jetties, boat ramps and popular accessible foreshore areas within the affected region.

Alexandrium blooms occur globally with limited options for management and are likely to re-occur periodically within the Swan and Canning rivers, due in part to the alga’s ability to produce long-lasting seed-like cysts. 

As part of the incident management team responding to the bloom, the Department of Biodiversity, Conservation and Attractions (DBCA), Department of Health, and Department of Primary Industries and Regional Development will continue to collect samples and monitor the bloom, seek faster testing methods, and explore possible management and control options.

Read detailed FAQs on the Alexandrium algal bloom and paralytic shellfish poisoning (external site). A map detailing affected waterways can be viewed on the DBCA website