The Department of Health is advising people not to eat fish, crabs or shellfish collected from within the Swan River, extending from the Royal Perth Yacht Club, Matilda Bay, upstream to the Garrett Road Bridge.
This area includes the commonly known areas of Matilda Bay, Perth Waters, Elizabeth Quay, Barrack Street Jetty, Claisebrook Cove and Ascot Waters.
This warning follows recent testing which has confirmed potentially toxic microscopic algae at elevated levels. It may be distinguishable in some areas by a red discolouration in the water.
Acting Environmental Health Executive Director Dr Michael Lindsay said that ingestion of toxins produced by the detected microscopic algae ‘Alexandrium spp.’ could produce a type of poisoning known as paralytic shellfish poisoning (PSP).
“These algae, which are not visible to the naked eye, can produce a toxin which could be absorbed by filter feeding shellfish and potentially consumed by crabs and finfish to a lesser extent,” he said.
“It is important to note that cooking will not destroy these toxins.”
People who consume wild shellfish, crabs or fish collected from this affected Swan River area 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.
Dr Lindsay said that anyone who had consumed shellfish, crabs or fish collected from the Swan River and experiences any of these symptoms should seek urgent medical attention, particularly if they feel any respiratory distress.
“Do not discard uneaten portions of mussels or other shellfish as these may assist with determining a likely cause of any symptoms.”
Shellfish includes oysters, mussels, clams, pipis, scallops, cockles and razor clams.
As a general rule people should avoid eating wild shellfish collected recreationally as their safety cannot be guaranteed. This is particularly the case for rivers, estuaries or other waterways where there is an increased likelihood of contaminant or nutrient inputs that in turn can 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 are not likely to be 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 will be erected at key locations including the Narrows Bridge, Garrett Road Bridge, certain boat ramps and accessible foreshore areas within the affected region.
This alga has occurred in the river in the past. Its current prevalence at concentrations of concern is attributed to suitable temperature and 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 and provide advice to the Department of Health.
Not all waterways are always 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.