KANGAROO ISLAND, SA – The shores of South Australia are in crisis. A catastrophic algal bloom — fueled by warming oceans and calm marine conditions — is killing marine life on an unprecedented scale, prompting experts, beachgoers, and government officials alike to describe the event as an unfolding “marine apocalypse.”
Since late March, residents and scientists have observed mass deaths of fish, shellfish, sharks, seadragons, rays, cuttlefish, and deepwater species along the southern coastline — particularly the Fleurieu Peninsula, Kangaroo Island and Goolwa. Dead seadragons (weedy and leafy), a protected species and an icon of the region’s biodiversity, have washed ashore in record numbers.
At the centre of this catastrophe is a toxic algal bloom of Karenia mikimotoi — a harmful dinoflagellate that thrives in warm, stagnant water and emits toxins lethal to marine life.
Climate Change Behind the Crisis
Scientists and government officials say the bloom is a direct consequence of record-breaking marine heatwaves, which have raised sea surface temperatures in South Australia by 2.5°C to 3.2°C above average since September 2024. One of the worst droughts on record is crippling multiple southern states. Adelaide has only received around 300mm of rain since February last year — the city’s driest 15-month spell since records began in 1839. Similar shortfalls are extending across the whole of agricultural SA, while severe drought is also impacting most of the western parts of Victoria and Tasmania.
South Australian Environment Minister Susan Close, has been sounding the alarm on the impacts of climate change in relation to the crisis and confirmed that ocean monitoring shows the bloom extending across an area roughly the size of Kangaroo Island and up to 20 metres deep.
“We are witnessing a full-scale climate emergency in our coastal waters,” Minister Close said. “These extreme marine heatwaves are not just anomalies — they are the new reality. And our marine ecosystems are the first casualties.”
“Unfortunately, as the world fails to fully come to grips with climate change we are likely to see more of this kind of experience”.
The bloom’s persistence is attributed to weeks of unusually calm conditions, low wind, and limited wave action, which have allowed the algae to thrive undisturbed.
Eyewitness Accounts: A Chronicle of Collapse
One of the most detailed personal records comes from accounts published in the Islander – Kangaroo Island), by Hugh Rischbieth, a beach walker at Island Beach who began chronicling the unfolding disaster in late March. In his words, the past six weeks have been “unlike anything I’ve ever seen.”
- On March 27, he noticed the first signs: discoloured water at Browns Beach.
- By March 29, rays were swimming ashore to die. He buried over 160 rays in the following days.
- On April 6, he collected a King George whiting and other species for testing.
- By April 8, cockles, razorfish, abalone, and bubble shells were washing up en masse, alongside larger deepwater fish like John Dory.
- On April 24, blue and ribbed mussels died off, followed by a massive crab die-off the next day.“We are seeing every layer of marine life perish — from the smallest worms to sharks and seadragons,” he said. “I don’t know what will recover and what won’t.”
- Most recently, on May 5, Rischbieth collected 10 weedy seadragons in a single 100-metre stretch. Thousands of pipefish were also found dead — a species not previously affected.
Mass Death Across the Coast
Other regions are reporting similar devastation:
- Snellings Beach was blanketed in salmon, flathead, swallowtails, and leatherjackets after recent northerly winds.
- At Stokes Bay, the smell was so strong that beachgoers reported coughing and respiratory issues.
- Goolwa Beach saw an uncountable number of dead cockles, shared widely by the South Australian Recreational Fishers network.
- Eyre Peninsula residents have also reported sighting washed up dead Fairy Penguins and Mutton Birds – it is unknown yet if these are related to the algal bloom.
- Yorke Peninsula Health authorities have detected a waterborne toxin linked to the algal bloom off Yorke Peninsula that has forced at least six oyster farms to temporarily shut and quarantine up to ten million oysters.
For those who love the ocean, the grief is personal
Kangaroo Island former resident, Stephanie Luke, is currently visiting and witnessing the daily devastation washing up on Island beaches and described the impact of the algal bloom and overheating seas as “a marine apocalypse”.
“National Parks and Fisheries came down to remove the juvenile bronze whaler from Penneshaw beach today” (8thMay). “One of the guys from Fisheries said there were more dead sharks down at Min Oil Beach.”
“I asked how many and he clammed up looked uncomfortable. I nudged a bit more. “What five, ten, fifteen?”
“He looked me in the eye and said, ‘About 50’”.
“I drove over with a phone but instead of dead sharks, the beach was full of dead rays. All different sizes and varieties. There were also many flapping listlessly in the shallows with a handful of sharks drifting aimlessly – the National Parks guy said they float in then beach and die.”
There’s a pink colour on them that may be abrasion from the sand or the rash caused from the algae.”
“It’s bloody spooky having nature so up-close and vulnerable”, Luke said.
“We’ve seen every kind of life disappear from these waters,” said Rischbieth. “This is more than just a bloom. It’s a collapse.”
“We don’t know what will recover and what won’t,” said Rischbieth. “But I had to speak up. This is no longer just a natural event — it’s a crisis accelerated by climate change.”
Tour guide Roanna Horbelt, from Research and Discovery Coastal Tours on Kangaroo Island, said she’s never seen such a die-off of iconic, protected marine species, including both leafy and weedy seadragons. “Your help as citizen scientists is critical,” she said. “We need to document every death to understand the scale of this.”
Great White Sharks Fleeing the Bloom
In a disturbing twist, four great white sharks have reportedly stranded themselves on South Australian beaches in recent weeks — seemingly trying to escape the toxic waters. A 3.01-metre white shark found at Henley Beach on May 5 is currently under autopsy. Marine scientists are examining whether disorientation or respiratory failure linked to algal toxins may be involved.
An investigation has also been launched on the Fleurieu Peninsula after authorities euthanised 50 sick kangaroos close to the toxic algal bloom that forced the closure of many popular beaches.
Call for Citizen Science and Urgent Reporting
Gavin Mathews of RecFish SA is one of many urging the public to report marine deaths to PIRSA’s Fishwatch hotline (1800 065 522) and upload sightings to the SA Marine Mortality Project on iNaturalist.
More than 137 contributors have already submitted observations and photographs, helping scientists identify patterns and hotspots.
Marine biologist Janine Baker warns that the impact on seadragon populations may be long-lasting.
“These deaths are happening just before their breeding season,” she said. “Populations across southern and central SA have been dying since March — it could take years for them to recover, if they do at all.”
Health Warnings for the Public
While Karenia mikimotoi is not known to be toxic to humans through seafood consumption, health officials are urging people to avoid contact with discoloured water, foam, or areas with strong marine odours, due to risks of skin, eye, and respiratory irritation.
What Comes Next
Though cooler weather may help disperse the bloom in coming weeks, the underlying driver — warming oceans from climate change — remains unaddressed.
“It is a terrible thing for us to be experiencing. Unfortunately it is consistent with climate change. We’ve had a marine heatwave off the coast of South Australia about 2.5 degrees above the average expected temperature for a prolonged period of time; alongside this very still weather pattern.
“So unfortunately, as the world fails to fully come to grips with climate change we are likely to see more of this kind of experience,” said Minister Close.
Latest data shows solar and wind power accounted for 80 per cent of South Australia’s electricity. Australia, as a whole however, has continued to support unlimited growth in fossil fuel production and export in contradiction of the Intergovernmental Panel on Climate Change’s call for no new coal and gas projects.
By Tracey Carpenter
11 May 2025
Photos by Stephanie Luke