The latest outbreak of toxic algae in the Swan River is the worst ever recorded occurrence of its species, according to a government department.
Department of Biodiversity, Conservation and Attractions river systems manager Peter Adkins said the toxic Alexandrium spp algae had bloomed for more than a month.
“We have seen Alexandrium before, but nowhere near the densities and the extent that we’ve seen in this instance,” he said.
Mr Adkins said the department was keeping an eye on its spread and finding ways to control it.
“We are starting very soon to undertake some laboratory trials into different approaches to control the bloom,” he said.
The DBCA takes samples from the river to a laboratory to analyse them for nuisance or toxic species of algae.
The DBCA then communicates the results to the Department of Health and other stakeholders.
The three departments then work together to determine if there is an issue and what to do.
Mr Adkins said big weather events may break up the bloom.
“What we’d need to see is either a large rainfall event to flush the bloom out or a change in the salinities and temperature, or a lot of really, really windy conditions to break up the bloom,” he said.
The algae can appear patchy with a red discolouration and cause water to look murky.
Algae is natural in the river system but a toxic algal bloom is uncommon.
The DBCA has not seen the bloom negatively affect wildlife.
The Department of Health said Perth residents should not eat marine wildlife from the river.
A spokesperson for the health department said there had been no additional health warnings or concerns for people.
Water temperature, salinity and significant tidal movements in the last few months contributed to the algae’s spread.
Mr Adkins said the algae would keep blooming as long as the river’s temperature and salinity contributed to its spread.
The DBCA monitors the water quality of the Swan Canning Rivers weekly.
It also monitors algal blooms to understand their impact on the river.
“There are a number of nuisance and toxic algal species which are present in the river system,” Mr Adkins said.
“But through our regular monitoring program, we keep an eye on them.
“Given the right conditions in the future, the [Alexandrium spp] bloom could potentially return.”