The Department of Health is reminding people over the Easter break and school holidays not to eat fish, crabs or shellfish collected from the Swan River downstream from Pelican Point to Como Jetty and upstream to Maali Bridge Park, Herne Hill.
Ongoing monitoring of the Swan River shows elevated levels of the potentially toxic microscopic algae 'Alexandrium minutum' still persist from Pelican Point to Como Jetty and upstream to Herne Hill.
This area includes the commonly known areas of Matilda Bay, Como Jetty, Perth Waters, Elizabeth Quay, Barrack Street Jetty, Claisebrook Cove, Ascot Waters, Riverside Gardens, Garvey Park, Sandy Beach Reserve, Point Reserve, Fish Market Reserve, Woodbridge Riverside Park and Middle Swan Reserve.
Acting Environmental Health Executive Director Dr Michael Lindsay said that ingestion of toxins produced by the detected microscopic algae 'Alexandrium minutum' could produce a type of poisoning known as paralytic shellfish poisoning (PSP).
"These algae, which are not visible to the naked eye, can produce toxins which can 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."
The Department of Biodiversity, Conservation and Attractions has conducted testing for toxins in mussels, Blue Swimmer Crabs and Black Bream in the Swan River, with assistance from the Department of Primary Industries and Regional Development, to help inform advice provided by the Department of Health.
To date, Paralytic Shellfish Toxins (PSTs) have been detected in some mussels and Blue Swimmer Crabs within the area affected by the Alexandrium minutum bloom. Based on these results and ongoing phytoplankton monitoring, the current advice not to eat fish, crabs or shellfish taken from the affected area in the Swan River remains in place.
People who consume wild shellfish, crabs or fish collected from the 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 shellfish collected recreationally in 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 have been erected at key locations including certain jetties, boat ramps and key accessible foreshore areas within the affected region.
This alga has occurred in the river in the past, but at far lower levels. 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 may be distinguishable in some areas by a red discolouration in the water.
It is not known how long the bloom will persist, but the Department of Biodiversity, Conservation and Attractions (DBCA) will continue to monitor algae levels within the Swan River.
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.
