News
The harmful algal bloom that is destroying South Australia’s marine wildlife is a climate disaster delivered with horrific clarity to our shores. By Jennifer Mills.
SA’s algal bloom disaster: The brutal reality of the climate crisis
For the past four months, an ecological catastrophe has been playing out along South Australia’s coast. A harmful algal bloom has been killing marine animals, spreading and growing with the currents and conditions. An overwhelming variety of species, including rays, sharks and cephalopods, are affected. The brutal reality of the climate crisis is washing ashore.
In mid March, surfers on the Fleurieu Peninsula emerged from the water with stinging eyes, blurred vision and persistent coughing. Discoloured foam was piling up on the beach. Dead marine animals had washed up too: fish, leafy sea dragons. The normally unspoilt coast at Waitpinga and Parsons Beach had turned rank.
By May, sharks were appearing unusually close to shore, sluggish and sickly. When a great white washed up on Henley Beach, concerned beachgoers attempted to move the shark back into the water, but it could not be saved. The bloom was present along the full stretch of Adelaide’s metropolitan beaches.
It has now spread from the northern coast of Kangaroo Island to the top of Gulf St Vincent. Its effects have reached from the Coorong to the Eyre Peninsula. It covers an area of about 4500 square kilometres – close to twice the size of the ACT.
Karenia mikimotoi is a natural presence in marine and fresh water, but several factors have contributed to its bloom. The floods of 2022-23 saw an unprecedented amount of fresh water and nutrients flowing through the mouth of the Murray River. An unusual upwelling the following year brought nutrients from the bottom of the sea to the surface. This year, consecutive high-pressure systems and an extended drought made for still and cloudless days.
The most significant factor is a persistent marine heatwave, says Professor Mehdi Doroudi, chief executive of South Australia’s Department of Primary Industries and Regions (PIRSA) and co-chair of a new taskforce set up to address the bloom. Since September, the local waters have been up to about 2.5 degrees warmer, he says, and “ecologically we should not be underestimating that”.
The world’s oceans are absorbing about 90 per cent of anthropogenic heat in the Earth system. According to a 2023 UNSW Sydney study, the Southern Ocean has seen the largest rise in heat storage over the past two decades. As well as more frequent marine heatwaves, the latest Intergovernmental Panel on Climate Change report predicted increases in the frequency and intensity of both flood events and drought.
Cooling winds finally arrived towards the end of May, but hopes they would break up the bloom were quickly dashed. A storm surge only brought more damage to the surface. Dead marine life has been strewn along the coast, including all of Adelaide’s city beaches: cuttlefish, rays, Port Jackson sharks, flathead, eels, pufferfish, razor clams, and more. Sea surface temperatures close to shore have now fallen, but deeper waters continue to experience conditions one to two degrees warmer than average.
While karenia mikimotoi is dominant, there are likely other similar species present. Brevetoxins harmful to humans have been detected on Yorke Peninsula oyster farms, and mikimotoi does not produce these toxins. Doroudi says shellfish are “the best bio-indicators in the ocean in terms of the movement of the algal bloom and any bio-toxins that are created”. Several pipi, oyster and mussel harvesting sites in the state have been closed while testing occurs. PIRSA has strict safety standards in place.
Algal blooms are lethal for marine life in a number of ways. A severe reduction of oxygen in the water will suffocate gilled animals. The toxins present in some algae can also create pathological symptoms, causing mechanical problems in gills, or even haemorrhages.
Citizen scientists have been active following a public call-out in April, says Brad Martin, who administers the SA Marine Mortality project on iNaturalist. The project has collected more than 14,000 observations of about 450 species. “That’s providing a huge amount of information that’s already being used in conversations with researchers and with government,” says Martin.
In the past month, high levels of algae have also been detected in estuarine waters, including West Lakes and the Port River, where 20 vulnerable bottlenose dolphins live in a precarious sanctuary. It is not thought that this bloom will affect mammals directly, but the National Parks and Wildlife Service has confirmed that 10 dolphins have been found dead elsewhere on South Australia’s coast since March 1.
“We’re having this ecosystem-scale impact where there’s a lot of stress on the marine environment,” Martin explains. “We’re seeing these massive fish kills so that means there’s less prey. There’s less visibility because of the algal bloom. We’re not seeing mass die-offs of [marine mammals], which is great, but just like everything else in the ecosystem there’s going to be impacts.”
Karenia mikimotoi is a dinoflagellate that can enter a cyst stage, resting in ocean sediments until conditions become favourable. As a result, blooms tend to recur, and with so many of SA’s coastal communities dependent on the twin industries of fishing and tourism, people are concerned about their livelihoods.
The loss of juvenile animals is particularly worrying. Doroudi says it’s too soon to announce fishing restrictions, but assessments are under way to determine a course of action. He pointed to existing interventions for abalone and snapper. Snapper fishing has been closed in half the state for the past six years.
Early indications are troubling. “There are fishers that are telling us that they haven’t been able to catch because of the algal bloom, especially around Kangaroo Island, Fleurieu Peninsula... They are saying that they can’t find fish,” Doroudi says. One Stansbury fisher told the ABC conditions on the sea floor are “like something you would see in a horror movie”.
After a similar bloom in Wellington Harbour, Aotearoa New Zealand, in 1998, oyster farming was shut down for a year as testing regimes were developed. PIRSA has been able to implement similar regimes quickly. The SA government has already waived fees for commercial fishers from April to June 2025, a gesture worth $500,000. But recovery from Wellington Harbour’s algal bloom took three to five years.
“Some species are going to recover quite quickly, others might not for a number of years,” says Martin. “The focus for us will be on ecosystem restoration, recovery and resilience.” Shellfish reef restoration may help to mitigate future blooms, while kelp forest and seagrass habitats support ecosystem recovery. “There’s a lot of community interest in doing coastal restoration in response to this,” he adds. Such efforts will need to be resourced.
As the beaches have become uncanny sites of grief, horror and confusion, conspiracy theories have arisen, pointing the blame at Adelaide’s desalination plant, the trucking of quarried sand to urban beaches, and even Chinese warships. SA opposition leader Vincent Tarzia has called for a royal commission, which the state Labor government argues would be a waste of time.
“There’s no question that this phenomenon occurred because of climate change,” SA Environment Minister Susan Close told ABC Stateline, describing the bloom as more prolonged and severe than anyone anticipated. “People ... need to appreciate that they can no longer rely on a stable and predictable marine environment,” said Close.
During this year’s Illuminate Adelaide festival, a group of Extinction Rebellion activists on an intersection of the city’s North Terrace held up a black banner: “CLIMATE CRISIS = OCEAN DEATH.” Two years ago, the state government quickly increased penalties for protesting after activists disrupted traffic outside an oil and gas conference on the same road. Though South Australia is a world leader in its transition to a renewable grid, the state government is still perceived as uncomfortably close to the gas lobby.
More actions are planned, including a “Hands Across the Sand” event organised by Greens Senator Sarah Hanson-Young. Her call for a national disaster to be declared is supported by the state government.
On Monday, the federal environment minister, Murray Watt, visited the state to inspect the damage. He announced $14 million to support fishers, “community awareness” and scientific research – an amount the state government pledges to match. Nevertheless, it is a drop in the ocean. Watt is the same environment minister who in May approved an extension of Woodside’s gas processing plant in Western Australia to keep it operating until 2070. Analysis by The Australia Institute has shown that the greenhouse gas emissions from this single project would almost equal those of Australia’s coal plants combined, helping to lock in future warming. At time of writing, Watt’s office had not responded to a request for comment.
This article was first published in the print edition of The Saturday Paper on July 26, 2025 as "On the beach".
For almost a decade, The Saturday Paper has published Australia’s leading writers and thinkers. We have pursued stories that are ignored elsewhere, covering them with sensitivity and depth. We have done this on refugee policy, on government integrity, on robo-debt, on aged care, on climate change, on the pandemic.
All our journalism is fiercely independent. It relies on the support of readers. By subscribing to The Saturday Paper, you are ensuring that we can continue to produce essential, issue-defining coverage, to dig out stories that take time, to doggedly hold to account politicians and the political class.
There are very few titles that have the freedom and the space to produce journalism like this. In a country with a concentration of media ownership unlike anything else in the world, it is vitally important. Your subscription helps make it possible.
Subscriber exclusive
Send this article to a friend for free.
Share this subscriber exclusive article with a friend or family member using share credits.
