The Department of Health is advising people not to eat fish, crabs or shellfish collected from within the Swan River, extending from Pelican Point to Como Jetty and upstream to Tonkin Highway Bridge. This area includes the commonly known areas of Matilda Bay, Perth Waters, Elizabeth Quay, Barrack Street Jetty, Claisebrook Cove, Maylands Yacht Club, Ascot Waters and Riverside Gardens.
This warning follows recent testing which has confirmed potentially toxic microscopic algae at elevated levels.
Acting Environmental Health Executive Director Dr Michael Lindsay said that ingestion of toxins produced by the microscopic algae Alexandrium species could produce a type of poisoning known as paralytic shellfish poisoning (PSP).
“The individual algae which are not visible to the naked eye, can produce a toxin which can be absorbed by filter feeding shellfish and consumed by crabs and fish to a lesser extent. It may be distinguishable in areas where it occurs in high concentrations by a red discolouration in the water. ” Dr Lindsay said.
“It is important to note that cooking will not destroy these toxins.”
People who consume wild shellfish, crabs or fish collected from the affected area of the Swan River may experience symptoms including:
- tingling or numbness of the lips
- prickliness of the fingertips and toes
- nausea or vomiting
- impaired balance
- slurred speech
- double vision
- 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.
Dr Lindsay said that anyone who had consumed shellfish, crabs or fish collected from the affected area of the Swan River and experiences any of these symptoms should seek urgent medical attention, particularly if they have difficulty breathing.
“Do not discard uneaten portions of mussels or other shellfish as these may assist with determining a likely cause of any symptoms,” he said.
Shellfish includes oysters, mussels, clams, pipis, scallops, cockles and razor clams.
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 could lead to increased microscopic algae growth.
Dr Lindsay said farmed shellfish purchased in supermarkets and other commercial outlets in WA are not affected as there is a strict quality-assurance program to ensure they are safe for human consumption.
“Other recreational activities including swimming, skiing and boating in the Swan River 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 jetties, boat ramps and key accessible foreshore areas within the affected region.
Alexandrium sp. bloomed over a large area of the Swan River for several months earlier this year, and its reemergence is of concern. The exact cause of the bloom is not known but predisposing factors may include a combination of water temperature, salinity, available nutrients, calm water conditions with limited mixing and low rainfall.
It is not known how long the bloom will persist, but the Department of Biodiversity, Conservation and Attractions will continue to monitor algae levels within the Swan River.
Not all waterways are monitored for algal blooms and anyone who sees or suspects an algal bloom in a waterway should report this to the Department of Water and Environmental Regulation’s ALGALWATCH during office hours on 6250 8064 or to the relevant local government authority for assessment.