What is happening with SA's algal bloom and why should the rest of Australia care?

Australia Broadcast Center

23-07-2025

South Australia is dealing with an "unprecedented" environmental disaster, which has spread throughout the coastline, killing thousands of sea creatures and taking a toll on businesses, tourism and the mental health of those who live and work near the sea.
Authorities and scientists say climate change has been a key driver in the algal bloom and warn the bloom is unlikely to go away anytime soon.
Here's what we know so far.
What causes algal blooms?
UTS marine biologist Shauna Murray told the ABC earlier this year that marine phytoplankton were generally a good thing for the environment, creating up to a half of the world's oxygen.
But a small percentage of the more than 100,000 different species of microalgae are harmful or toxic.
What is the algal bloom in South Australia?
The harmful algal bloom dominating South Australia's coastline is Karenia mikimotoi . In low numbers, the microscopic algae cannot be seen by the naked eye.
Here's what it looks like under a microscope:
The samples that showed karenia mikimotoi to be present in the Coorong were collected by Glen and Tracy Hill. ( Supplied: Faith Coleman )
"So, they're not visible as cells to the naked eye, but you can see the colouring, so when they're extremely abundant you can see a sort of slight … water discolouration that is reddy, brown … but not always," UTS researcher Shauna Murray told the ABC earlier this year.
And from the coastline, it can wash up a brown-coloured foam, which looks like this:
The algae produced large amounts of foam again at Knights Beach at Port Elliot over Easter. ( ABC South East SA: Caroline Horn )
How did the bloom begin?
SA Environment Minister Susan Close said the outbreak followed three key events.
In 2022/23 the state experienced flooding along the River Murray, which saw run-off enter the Southern Ocean.
Here's an image of the run off from above:
After that, in 2023/24 a cold upswelling brought nutrient rich water to the surface.
And in September 2024, a marine heatwave began, which saw temperatures 2.5 degrees Celsius above normal levels.
On March 15, surfers and beachgoers reported illnesses after visiting Waitpinga Beach on the Fleurieu Peninsula.
By March 16, a brown foam and dead sea life was found on the beach, marking the beginning of a months-long crisis along SA's coastlines.
Dr Close said all of those events could be attributed to climate change.
What does the algal bloom do to humans?
Health authorities say contact with Karenia mikimotoi can cause flu-like symptoms, including skin rashes and respiratory symptoms, but no long-term health impacts.
For surfer Anthony Rowland, who first felt the impact of the bloom at Waitpinga Beach, it started as a tickle in his throat and then progressed to a cough.
Anthony Rowland said he felt as though authorities did not take his initial reports seriously. ( ABC News: Che Chorley )
He reported other surfers in the area having blurred vision, wheezing and sore throats.
How do you treat algal bloom sickness symptoms?
SA Health's advice is to stay out of waters where the bloom appears to be present, but if you do come into contact with it to leave the area and wash yourself.
"If symptoms are more severe or do not resolve, seek medical advice from a GP and call 000 if it is a medical emergency," SA Health states on its website.
How does it kill fish?
Professor Murray said the algae affects fish gills and skin.
" Karenia mikimotoi doesn't actually produce a toxin but it does produce what's called reactive oxygen species so this can damage the gills of fish and it can affect skin cells," she said.
"What this damaging the gills of the fish means is marine animals basically drown if their gills become too damaged."
A globe fish on the beach at Waitpinga, south of Victor Harbor, after the initial outbreak in March. ( ABC South East SA: Caroline Horn )
Other dead sea mammals have been found dead along the coast, including dolphins and sea lions.
The official advice is that Karenia mikimotoi isn't toxic to mammals.
The government said it was not uncommon for marine mammal carcasses to wash ashore after winter storms.
SA authorities are performing autopsies to determine the cause.
Where is the algal bloom at the moment?
As of July 18, authorities say the bloom is present in the Gulf Saint Vincent, which covers many of Adelaide's metropolitan beaches, as well as areas in the Fleurieu Peninsula and the Spencer Gulf.
This satellite image shows levels of chlorophyll a in red, which is an indicator of the bloom's presence:
A July 16, 2025, sea surface map of chlorophyll-a levels on the South Australian coast, which can indicate algae concentrations. ( Department of Primary Industries and Regions SA )
On Wednesday, a dead sea turtle found at Glenelg was among the latest casualties.
What kills an algal bloom?
According to the latest science, nothing can be done to dilute or dissipate the bloom.
When it first appeared, scientists predicted a cold winter front would help dissipate it.
But the ongoing marine heatwave and drought conditions meant rain did not arrive until winter, and the storm fronts have done little to hamper the bloom so far.
A birdseye view of the algal bloom in waters off the Fleurieu Peninsula. ( ABC News: Che Chorley )
There have been some glimmers of hope though. Estuarine ecologist Faith Coleman detected Noctiluca scintillans — the algae which causes "sea sparkle".
"What they do is they go round, they eat other bacteria and algae, and in this case it looks like they're probably eating Karenia mikimotoi ," Ms Coleman said.
Is it safe to eat fish?
Fishing businesses and scientists have told the ABC catches are down 50 per cent in some parts of the state, but for those still fishing, business is also being impacted by the news of the bloom.
SA Environment Minister Susan Close said she would be looking at further measures to remind consumers that fish for sale was still safe to eat.
"SA Health advises that fish caught live are safe to eat," PIRSA's website states.
"However, SA Health does not recommend people eat fish or cockles found dead because of likely spoilage and decomposition."
South Australian Fisherman Co-Operative Limited manager Ian Mitchell told the ABC earlier this week he had "fishermen in tears on the phone", but the mood was better following the announcement of state and federal funding.
This week, the federal government announced $14 million in funding to help South Australia deal with the algal bloom outbreak, but stopped short of declaring it a national disaster.
On Tuesday, the SA government said it would match federal funding, with the resources to go to helping impacted industries, further research and monitoring and holding public community information forums.
"The feeling was a lot better today than the last three months. There was a fair bit of fish considering the weather was pretty poor, and prices were up a little bit so it seems like the public is listening to, you know, it is safe to eat," Mr Mitchell said.
What has the impact been and what's next?
The bloom has killed thousands of sea creatures, decimated local sea habitats and has spread at an unprecedented level.
It has had a huge impact on commercial fishing, tourism and other businesses who operate in or near the sea.
The fish kills have been a hot topic on the island since the beginning of the algal bloom outbreak. ( ABC News: Che Chorley )
The toll on those who work in the space has also been significant.
So what's next?
Flinders University Associate Professor of Natural Sciences (Oceanography) Jochen Kaempf has developed a computer model to predict where the algae will spread next.
While awaiting peer review, the model predicts the bloom will ease over winter, but worsen next summer.
"There is nothing you can actually do to prevent it. The only thing you can do is you can hope that there is enough of the zooplankton, which are swimming, small marine plankton that actually eat, take up enough of the algae so that it can't re-evolve in the next summer when the water gets warmer again," Professor Kaempf said.
"The only thing that can actually only clear it up is if it's consumed, if it's eaten by other marine organisms of the food chain."