A dead razor fish on Semaphore beach found earlier this month amid the toxic algal bloom.(ABC South East SA: Caroline Horn)
A toxic algal bloom off South Australia's coast is unlikely to end quickly despite cooler temperatures and winter storms, the state government warns.
The bloom is now impacting metropolitan Adelaide beaches, with reports of dead sea creatures from North Haven to Aldinga.
Environment Minister Susan Close says "we are helpless in the force of nature", warning that the bloom is likely to recur, even if it dissipates.
A damaging algal bloom off South Australia's coast that is killing marine life is unlikely to dissipate anytime soon, with the South Australian government warning there "isn't much we can do" to fix the problem.
The toxic bloom, firstdetected in March off the Fleurieu Peninsula, has been plaguing South Australia's coastline in the past three months, responsible for discoloured water and foam and countless dead creatures that have washed up on shore.
The bloom's impact has reached metropolitan Adelaide beaches, with locals capturing images of deadsharks and sea lions.
Scientists werehoping that a drop in temperatures over winterwould bring an end to theecological disaster,which appeared after a range of environmental impacts hit the region, including water from the 2022/23 River Murray floods flowing into the Southern Ocean, followed by unseasonably cold and warm water.
But Environment Minister Susan Close said despite ongoing storms and cooler temperatures, "we are seeing the algae being very persistent".
She said she wanted to "prepare people" that the bloom was "not something that is likely to pass quickly" and "likely also to return at some point".
An image of a dead shark which washed up at Hallett Cove Beach last week as SA's toxic algal bloom spread to metropolitan beaches.(Supplied: Jacob Klotz)
"We've seen the large mass of algae — the depth of some 20-metres and the size of Kangaroo Island — break up significantly," she said on Monday.
"But what's happened, is a lot of it has just been moved around into other parts of South Australian waters, including the metropolitan coast.
"This is of concern … because we're continuing to see marine life washing up dead on our coastline."
Satellite mapping of South Australia's coastline shows high levels of chlorophyll-a along the eastern side of Gulf St Vincent.
Sea surface chlorophyll-a map taken on June 23, 2025, which indicates algae concentrations along the SA coastline.(Supplied: SA Government via https://oceancurrent.aodn.org.au/)
While the mapping is an indicator of the likelihood of the presence of the bloom, Dr Close confirmed metropolitan Adelaide beaches were now bearing the brunt of the bloom.
Asked if the government was prepared for this, Dr Close said some movement of the bloom was anticipated.
"We were expecting that as the big winds came in and the waves started moving around more that it would move around," Dr Close said.
"Therefore, we're not exempt in the metropolitan beaches, it wasn't surprising, but it's hard to predict exactly where the currents are going to take the bloom at any given time.
"It may well be discovered at some point in the Port River. It may even make its way into West Lakes."
The government believed the bloom was unlikely to dissipate quickly because an "ongoing marine heatwave" was continuing off SA's south coast.
Further complicating matters, Dr Close said, was that the species responsible for the bloom,Karenia mikimotoi,can drop to the seabed and survive if the conditions no longer suited it.
"What that means is we've got a lot of those dinoflagellates that will be dropping to the ocean floor because we've had such a large bloom," she said.
Hundreds of cockles were found washed up on Goolwa Beach in April amid the toxic bloom.(Supplied)
After it was firstreported around Waitpinga and Parsons beachesin March, the algal bloom spread to Kangaroo Island, Yorke Peninsula and the Coorong.
The bloom is considered non-toxic to humans, but can cause skin, eye and lung irritation.
A mysterious, brown foam appeared on a beach an hour south of Adelaide. It was just the beginning of a toxic algal bloom that grew to thousands of square kilometres in size, killing precious sea life in its wake.
Dr Close said the bloom was causing a "widespread number" of marine deaths and also putting "some of our most vulnerable and precious species … at risk".
But she warned that there was not "much we can do" about the situation other than building nature's resilience and continued monitoring.
"We can't control the movement of theKarenia mikimotoi bloom,that’s dictated by the way in which the oceans move,” she said.
"We can't kill it off — simply too much of it in too much of a large expanse of ocean.
"And unless we're talking about aquaculture inside nets, we can't move animals.
"We are helpless in the force of nature, and that is something that we as people need to understand our place in the natural world."
Estuarine ecologist Faith Coleman, who has been helping coastal communities understand the algal bloom, said her primary concern was that the bloom was becoming "more adaptable to the climate it's facing".
"The challenge is if it doesn't clear out this winter, and we still have enough organic matter remaining in the water column, there is a high probability that we're going to have a bloom that restarts again next summer," she said.
"That's a concern because the ecosystem has taken this hit, and getting another hit is likely for it to become an inter-annual or regular event."
Estuarine ecologist Faith Coleman says the bloom could last for 18 months if it does not clear this winter.(ABC South East SA: Caroline Horn)
Ms Coleman highlighted California, which hasreportedly had algal blooms recur for four consecutive years, as an example.
She said some blooms lasted weeks, some three-to-four months and some 18 months.
"I am deeply concerned that since we have passed that three-to-four-month point with this … that we are looking at a bloom that will now go for 18 months if it doesn't clear this winter," she said.