2025 algal bloom in South Australia

Last updated

2025 South Australian Harmful Algal Bloom
Map
Marine areas affected by the bloom
DateMarch 2025–ongoing
Location
TypeMass fish kill
Cause Marine heatwave,
coastal upwelling
Website algalbloom.sa.gov.au/

A harmful algal bloom (HAB) event that started in March 2025 is ongoing along the coasts of the state of South Australia as of October 2025. It has caused fish kills impacting the marine environment and associated fishing and aquaculture industries, as well as beachgoers and tourism operators along the affected coasts. The state government has set up an information website and hotline dedicated to the event, and the state and federal governments are working together on mitigation of the bloom. Temporary fishing restrictions on certain species, starting 1 November 2025, have been imposed to allow them to recover. The environment ministers responsible are Lucy Hood (SA) and Murray Watt (federal).

Contents

The causes of the bloom are attributed to flooding of the River Murray in 2022-23 that brought extra nutrients into the sea; a cold-water upwelling in summer 2023-24 that lifted more nutrients to the surface; and a marine heatwave that has occurred since September 2024. These changes, particularly the latter, have been attributed to climate change. The algae are not considered a significant health concern, although people who experience an allergic reaction such as asthma, coughing, or itchy eyes should not stay in close proximity to foamy or discoloured water.

Background and extent

Sea foam at West Beach after a storm and following decay of an algal bloom in October 1996 Sea-foam-west-beach.jpg
Sea foam at West Beach after a storm and following decay of an algal bloom in October 1996

In March 2025, a marine heatwave-induced bloom, initially identified as consisting mainly of the dinoflagellate Karenia mikimotoi , was blamed for the deaths of thousands of marine creatures, as well as coughing, sore eyes, and blurry vision in humans, along stretches of beach along the south coast of the Fleurieu Peninsula in South Australia. [1] Despite hopes that winter storms would cause the bloom to dissipate, [2] relatively mild conditions (potentially attributed to climate change [3] [4] ) caused it to persist [5] and spread along adjacent coasts of Kangaroo Island and Gulf St Vincent (including Adelaide's metropolitan beaches [6] [7] ) and into the Coorong. [8]

By the middle of the year, the state government estimated the size of the bloom as around the same size as Kangaroo Island, which covers over 4,000 km2 (1,500 sq mi) (about 80 times the size of Sydney Harbour). [9] By October 2025, the bloom had spread on the currents, into both Gulf St Vincent (flanking the Yorke and Fleurieu Peninsulas) and Spencer Gulf, along the coast of the Eyre, as well as to Kangaroo Island itself. [9] Marine biologist Mike Steer, chief executive of the South Australian Research and Development Institute (SARDI), [10] estimates that it has affected around 30 per cent of the state's coastline, roughly equivalent to 1,500 km (930 mi). He said that its extent and duration is unprecedented in both South Australia and Australia, and is probably one of the top ten recorded blooms in the world. [9] The densest occurrence of the bloom, manifesting in foam, was occurring on the stretch down the coast from the top of Gulf St Vincent down to Brighton Beach. [11]

Species composition

Besides K. mikimotoi, other Karenia species including K. brevisulcata and K. longicanalis have been found to be present in the bloom, as well as others yet to be identified. [12] Collaborating with SARDI and independent local consultants, marine biologists from Flinders University, University of Technology Sydney and the University of Tasmania are involved in studying the bloom, with specialist marine toxicological expertise being sought from the Cawthron Institute in New Zealand. [12]

In November 2025 researchers announced that they had tentatively identified K. cristata as having been the dominant species present for much of the time in the bloom, and that this little-known species (one of five Karenia species present) is responsible for the brevetoxins detected in shellfish, and the probable cause of the respiratory symptoms experienced by surfers when the first reports of the bloom were made in March. [13]

Possible causes

It was at first thought likely that flooding that occurred in 2022–23 which washed nutrients down the Murray–Darling basin (which covers a large area across several states and territories of Australia into the sea at the Murray mouth on the south coast of South Australia, combined with a marine heatwave and an upwelling of nutrients from sea floor, created "perfect conditions" for K. mikimotoi to flourish. [14] However, scientists later said that this was an unlikely cause, as the time lag between the events was too great. [15]

According to the government website, the bloom has been building up over time, and its causes may be attributable to the following events: [16]

According to the not-for-profit Biodiversity Council, [a] marine ecologists have warned that ocean warming and marine heatwaves associated with climate change, as well as nutrient pollution, have led to a rise in the number of algal blooms, and this is likely to continue. Large areas of kelp, seagrass, and shellfish reefs, which tend to filter nutrients, have been lost. In addition, the gulfs around the South Australian peninsulas, especially Gulf St Vincent, are more susceptible to HABs because they have less water exchange than open ocean coastlines, and the water is shallower, which increases its heating capacity. [18] The Australian Marine Conservation Society agrees with the assessment that climate change has driven the bloom, calling the event a "crisis" and a "warning we can’t ignore". [19]

Claims that the bloom may have been caused by the Adelaide Desalination Plant have been dismissed by researchers as misinformation. [3]

Impact

Although not produced by K. mikimotoi, brevetoxins produced by other Karenia species have been detected in commercial shellfish farms, leading to temporary closures, [20] and in foam washed up on beaches, with health authorities issuing advice for asthmatics. [21]

The bloom has killed more than 500 species [18] [22] of fish, penguins, [23] and marine mammals, and has also caused health problems such as asthma, skin and eye irritation, and coughing in humans. [24] It has affected the aquaculture, [16] fishing and tourism industries, especially local fishers, as well as the many residents who live along the coastline and surfers who frequent popular surfing spots such as Port Elliot. [9] Several groups of First Nations peoples have called the ongoing bloom a "cultural emergency". The Narungga people of Yorke Peninsula have been heavily affected by the bloom. [25] The Goolwa Pipi Co., which harvests a small edible saltwater clam known as the Goolwa pipi, was no longer able to harvest and sell their shellfish. [26]

It was feared that the bloom would affect the breeding season of the unique population of giant cuttlefish in the northern Spencer Gulf, in a sanctuary area that received National Heritage status in 2023, the Cuttlefish Coast Sanctuary Zone. This population of the species is even distinct from the population in the southern Spencer Gulf, and the only population of giant cuttlefish in the world to breed in a mass event, in a spectacular display of colours, including blue, purple, green, red and gold, which change as they mate and lay eggs. This makes it a popular tourist attraction. [27] See below for the device created by SARDI to protect some of the cuttlefish, an air-bubble curtain generator.

In the seven days preceding 3 October 2025, clearing of beaches along the coast collected around 1,600 kg (3,500 lb) of marine animals, including longsnout boarfish, whiting, and leatherjacket fish. The previous week of hand-clearing netted a total of two tonnes of dead sea life. [26]

According to head of SARDI Mike Steer on 3 October 2025, the algae and the brevetoxins they produce are "not significant health concerns", and there is no need to stay away from the water. He himself has continued to surf. However, if the water is discoloured or foamy, and a person is susceptible to itchy eyes, coughing, or other irritation, they should move away. [28]

The local seafood industry has suffered a downturn, despite assurances that fish caught in SA waters are safe to eat, and many fisheries have been completely unaffected by the bloom; consumer confidence dropped owing to the news describing the bloom as "toxic" or "harmful". [29] [22]

It was discovered in late October that, according to SARDI data, that the numbers of squid, garfish, and King George whiting had been severely depleted in Gulf St Vincent and around Kangaroo Island, while some other species, such as blue crabs, had also declined. [30]

Responses and suggestions

Government responses

The state government briefed federal Environment Minister Murray Watt on 11 June 2025, who engaged with engaged with then state environment minister Susan Close during the following months. At that time, the HAB was expected to dissipate over the winter months. [31]

The state government has created a website to provide information to the public, [32] and has issued vouchers to encourage tourists. [33] To complement the website, a telephone hotline was launched on 2 October 2025, to be used for general information, reporting dead fish or other animals, getting health advice and mental health support, and information about support packages. [11]

On 9 September, SA Health issued updated public health advice, saying that people with asthma should carry medication when visiting beaches when foam is present. [21] SA Health is also providing mental health support for those affected by the HAB. [34]

The state and federal governments have provided A$28 million in funding to support research, clean-up efforts, community support, industry help, and public information. [32]

A support package for small businesses affected by the HAB is being provided by the state government, which includes a one-off Algal Bloom Fisheries and Aquaculture Assistance Grant of up to A$100,000 as well as a A$10,000 Algal Bloom Small Business Support Grant, for smaller businesses or not-for-profits. [35]

In August 2025, the state and federal governments provided funding of almost $700,000 to install a bubble curtain to protect the giant cuttlefish in the Upper Spencer Gulf during their breeding season, should the bloom move into that area. The curtain would protect approximately 50,000 to 80,000 eggs and hatchlings. [36] The air-bubble curtain generator devised by SARDI would protect a small section of the cuttlefish breeding ground near Point Lowly from incursion of harmful algae. The 200 by 100 metres (660 ft × 330 ft) apparatus, driven by an on-shore compressor, was expected to provide a barrier, not as a remedy or cure, and would be energised when the breeding ground is threatened. A small proportion of the season's eggs would be protected, to become the new breeding colony when the water is safer. [37]

On 3 October 2025, the state and federal governments announced a $1.4 million program to protect Australian sea lions, which are an endangered species of which 80 per cent live in South Australian waters. [26]

An allocation $850,000 was pledged by the state government to fund the restoration of 15 oyster reefs around Yorke Peninsula, Eyre Peninsula, and Kangaroo Island over three years. [38] Some of this funding is allocated to the creation of 25 additional sites as part of a reef restoration project started in 2023 by Eyre Lab director Manny Katz and University of Adelaide research fellow Dominic McAfee. Volunteers, including children, are assisting in the project. [39]

The state government imposed temporary fishing restrictions several species from 1 November 2025, to allow their numbers to recover. The restrictions included a 50 per cent reduction in bag and boat limits for charter boat fishing in the Gulf St Vincent/Kangaroo Island Fishing Zone, and a 50 per cent reduction in bag and boat limits to squid, garfish, blue crab, and King George whiting in the Spencer Gulf Fishing Zone. There are also temporary restrictions on all commercial marine scalefish fishing and blue crab fishing in the Gulf St Vincent/Kangaroo Island Fishing Zone. [30]

Summer plan and other support

Surf Life Saving beach patrols funded by state and federal governments are to be posted at eight beaches seven days a week all through the summer, showing safe places to swim between flags on the beach. A new Beachsafe app was launched on 12 October. [40] Clean-up crews funded by the SA government will inspect around 23 coastal locations between North Haven to Goolwa daily. On 13 October, the state and federal governments launched the $15m "Coast is Calling – Dining Cashback program", which offers $50 to up to 300,000 people dining at beachside establishments. [41] On 14 October, the SA Government announced a $16m support package for fishing and marine industries, offering grants of up to $275,000 to each eligible business. On the same day, the state and federal governments jointly announced their Algal Bloom Summer Plan, which includes $102.5 million in total to address the problem, which includes: $20.6 million towards environmental restoration; $17.3 million for monitoring and research; $48 million for businesses and communities along the coast; and another $16m to boost recreation and tourism at the coast. [42]

Senate inquiry

A Senate inquiry was set up on 23 July 2025, with the Senate Standing Committees on Environment and Communications due to publish its report on 28 October 2025. [43] On the opening day of the inquiry, the committee heard that the state was unprepared for the disaster. [21] It has held public hearings in Adelaide, Port Lincoln, Ardrossan, and Victor Harbor. [15] Kaurna Yerta Aboriginal Corporation, in its submission to the inquiry, said that the government's response had been "too slow" and it had not engaged enough directly with First Nations people. [25]

Ongoing activities and situation

Premier Peter Malinauskas and new SA Environment Minister Lucy Hood continue to liaise with federal Environment Minister Murray Watt about a plan for managing the HAB through the summer. [11]

From early October, 94 coastal sites are being regularly monitored by the South Australian Research and Development Institute (SARDI). [11] The bloom is not present in the northern Spencer Gulf, the giant cuttlefish breeding ground. [11]

On 4 November 2025, SARDI reported in its weekly update that there was no Karenia detected at 14 out of 21 metropolitan onshore sites, and the rest recorded low levels. This had reduced considerably from 21 October, when six sites showed over a million cells of Karenia per litre. [44]

Other suggestions

Donald Anderson, the director of the US National Office for Harmful Algal Blooms at the Woods Hole Oceanographic Institution, who has been consulted by the state government, has described a treatment involving a form of modified clay. [12] The substance can be sprayed into the water, where it sticks to the algal cells, creating clumps called "floc", which fall and settle on the sea floor. [14] While this treatment may be effective on a small scale, the quantities of clay needed would be impractical over the 4,500 km2 (1,700 sq mi) affected area. [45]

The Australia Institute has suggested that a National Climate Disaster Fund, paid for by levies on coal, oil, and gas production, would save taxpayers the billions that needs to be spent on mitigation of disasters caused by climate change, such as the South Australian HAB. [46]

Volunteers

Volunteers are building 1,200 shellfish reef modules to place in the Port River, under the auspices of fish habitat charity OzFish. Most of the native oyster population around the state's coast had previously been destroyed by historic dredge fishing. [47] The oysters filter the water and improve its quality, reducing the likelihood of the HAB spreading in the river. [38]

Management

Marine ecologist Dominic McAfee, of the University of Adelaide, said that there is limited understanding on what impacts the HAB will have in both the short and long terms, and it is essential to first fill the gaps in knowledge in order to provide evidence-based management, monitoring, and an appropriate socio-economic response to recover from the event. [18]

Footnotes

  1. ↑ "...an independent expert group founded by 11 Australian universities to promote evidence-based solutions to Australia’s biodiversity crisis", whose lead councillors include Hugh Possingham [17]

References

  1. ↑ "Microalgae toxic to fish identified as cause of bloom linked to Fleurieu Peninsula marine deaths". ABC News. 25 March 2025. Retrieved 25 March 2025.
  2. ↑ Horn, Caroline; Boisvert, Eugene; O'Brien, Samuel; Bermingham, Kathryn (30 May 2025). Hopes high after ocean temperatures off SA coast drop amid algal bloom outbreak ABC News . Retrieved 30 May 2025.
  3. 1 2 Haynes, Jessica; MacLennan, Leah; Chorley, Che (30 May 2025). An ecological disaster has been unfolding on Australia's coast ABC News. Retrieved 30 May 2025.
  4. ↑ MacLennan, Leah (5 July 2025). SA's toxic algal bloom is unlikely to end soon so what are the consequences? ABC News. Retrieved 5 July 2025.
  5. ↑ Horn, Caroline (20 June 2025). Micro algal bloom off SA persists as commercial fishers seek economic relief ABC News. Retrieved 20 June 2025.
  6. ↑ Landau, Sophie; Mason, Olivia; Horn, Caroline (28 June 2025). 'Heartbreaking' algal bloom hits metropolitan Adelaide beaches ABC News. Retrieved 28 June 2025.
  7. ↑ Horn, Caroline; Landau, Sophie; Brine, Josh (3 July 2025). Dead marine life from algal bloom collected from Adelaide beaches amid local extinction fears ABC News. Retrieved 3 July 2025.
  8. ↑ Horn, Caroline (4 June 2025). Marine algal bloom spreads to SA's Coorong as fishers find dead creatures in North Lagoon ABC News. Retrieved 4 June 2025.
  9. 1 2 3 4 Keane, Daniel; MacLennan, Leah; Chorley, Che (1 October 2025). "Australia's southern coast is in uncharted waters". ABC News. Archived from the original on 2 October 2025. Retrieved 2 October 2025.
  10. ↑ "Professor Mike Steer". Department of Primary Industries. 21 July 2025. Retrieved 3 October 2025.
  11. 1 2 3 4 5 "1800 BLOOM: New hotline launched amid calls for summer plan". InDaily . 2 October 2025. Retrieved 2 October 2025.
  12. 1 2 3 Phiddian, Ellen (29 August 2025). Scientists race to find weapons against South Australia's toxic algal bloom ABC News. Retrieved 29 August 2025.
  13. ↑ Horn, Caroline (5 November 2025). Karenia cristata species source of toxins in SA's algal bloom, scientists believe ABC News. Retrieved 5 November 2025.
  14. 1 2 Shepherd, Tory (24 August 2025). "South Australia scrambles to fight its pulsating algal bloom: 'We're trying to call on everybody that we can'". The Guardian. Archived from the original on 31 August 2025. Retrieved 2 October 2025.
  15. 1 2 Horn, Caroline (21 September 2025). "Murray River flood may not be to blame for SA algal bloom, Senate inquiry hears". ABC News . Archived from the original on 21 September 2025. Retrieved 29 September 2025.
  16. 1 2 "About the Algal Bloom". Algal Bloom Update. 1 May 2025. Archived from the original on 2 October 2025. Retrieved 2 October 2025.
  17. ↑ "About Us". Biodiversity Council Australia. 19 November 2024. Archived from the original on 11 August 2025. Retrieved 2 October 2025.
  18. 1 2 3 Rafalowicz, Joe (17 July 2025). "Experts outline human drivers of harmful SA algal bloom, and how we can better prepare for future". Biodiversity Council Australia. Archived from the original on 12 August 2025. Retrieved 2 October 2025.
  19. ↑ Arvela, Jess (24 July 2025). "South Australia's algal bloom crisis: a warning we can't ignore". Australian Marine Conservation Society. Archived from the original on 12 August 2025. Retrieved 2 October 2025.
  20. ↑ Yankovich, George and Graham, Narelle (8 May 2025). Toxin caused by algae forces quarantine of oysters on Yorke Peninsula ABC News. Retrieved 8 May 2025
  21. 1 2 3 Kelsall, Thomas (9 September 2025). "SA Health updates asthma advice on bloom, scientists say full extent of damage unknown". ABC News. Archived from the original on 19 September 2025. Retrieved 29 September 2025.
  22. 1 2 Keane, Daniel (13 October 2025). SA Premier says algal bloom is not 'toxic', despite word appearing in official government advice ABC News. Retrieved 13 October 2025.
  23. ↑ Pedler, Emma and Bailey, Duncan (9 May 2025). Dead little penguins washed up on multiple Eyre Peninsula beaches ABC News. Retrieved 9 May 2025.
  24. ↑ Merritt, Rachael (26 August 2025). "Algal bloom impacting mental and physical health along SA's coastal frontline, residents say". ABC News. Retrieved 27 August 2025.
  25. 1 2 Carbone, Isabella (16 September 2025). "SA's ongoing harmful algal bloom labelled 'cultural emergency' by First Nations groups". ABC News. Retrieved 21 September 2025.
  26. 1 2 3 Karakulak, Helen (3 October 2025). "Sea lion protection plan amid tonnes of dead sea life". InDaily . Retrieved 3 October 2025.
  27. ↑ Doubleday, Zoe (30 July 2025), Peddie, Clare (ed.), "The giant cuttlefish's technicolour mating display is globally unique. The SA algal bloom could kill them all", The Conversation (website) , doi: 10.64628/aa.mn534mhac , archived from the original on 3 September 2025, retrieved 2 October 2025
  28. ↑ Steer, Mike (3 October 2025). "The complicated messaging surrounding SA's algal bloom summer". ABC News (Interview). Interviewed by Bermingham, Kathryn. Archived from the original on 4 October 2025. Retrieved 4 October 2025.
  29. ↑ Brine, Josh (5 October 2025). "SA seafood demand still down as algal bloom safety message struggles to break through". ABC News. Retrieved 12 October 2025.
  30. 1 2 Gilchrist, Charlie (23 October 2025). "Data shows fish species decimated in SA waters". InDaily . Retrieved 24 October 2025.
  31. ↑ Merritt, Rachael (2 October 2025). "Glenelg beach blanketed with foam as Premier announces algal bloom hotline". ABC News. Archived from the original on 2 October 2025. Retrieved 2 October 2025.
  32. 1 2 "Home". Algal Bloom Update. 29 July 2025. Retrieved 27 August 2025.
  33. ↑ "New South Australia travel vouchers launched to support algal bloom impacted coastal communities". Glam Adelaide. 24 August 2025. Retrieved 27 August 2025.
  34. ↑ "Algal bloom mental health support". SA Health. 11 August 2025. Archived from the original on 2 October 2025. Retrieved 2 October 2025.
  35. ↑ "Algal Bloom Support Package". Office for Small and Family Business. 25 July 2025. Archived from the original on 12 August 2025. Retrieved 2 October 2025.
  36. ↑ Ntafillis, Viki (28 August 2025). "'Bubble curtain' to protect giant Australian cuttlefish from South Australia's toxic algal bloom". ABC News. Archived from the original on 25 September 2025. Retrieved 3 October 2025.
  37. ↑ "Lifting the (bubble) curtain on cuttlefish protection". State Government of South Australia. 12 September 2025. Retrieved 14 October 2025.
  38. 1 2 Dowdall, Rory (10 October 2025). "Hundreds of shellfish reefs ready to tackle algal bloom". InDaily . Retrieved 12 October 2025.
  39. ↑ Ganesan, Arj (28 October 2025). "The key role a 'lost' reef is playing in South Australia's algal bloom fight". ABC News. Retrieved 31 October 2025.
  40. ↑ Record beach patrols in South Australia this summer as life savers help battle algal bloom ABC News, 12 October 2025. Retrieved 12 October 2025.
  41. ↑ Karakulak, Helen (13 October 2025). "Algal bloom summer plan: $15m to bait South Aussies". InDaily . Retrieved 14 October 2025.
  42. ↑ Gilchrist, Charlie (14 October 2025). "Bloom support plan swells to more than $100m ahead of summer". InDaily . Retrieved 14 October 2025.
  43. ↑ "Algal blooms in South Australia". Parliament of Australia. 23 July 2025. Retrieved 29 September 2025.
  44. ↑ Gilchrist, Charlie (5 November 2025). "Signs of algal bloom 'clearing up' as likely cause revealed". InDaily . Retrieved 5 November 2025.
  45. ↑ Kelsall, Thomas (21 August 2025). US algal bloom expert suggests modified clay as mitigation measure for SA outbreak ABC News. Retrieved 21 August 2025
  46. ↑ "SA algal bloom underlines urgent need for National Climate Disaster Fund". The Australia Institute. 18 August 2025. Archived from the original on 2 October 2025. Retrieved 2 October 2025.
  47. ↑ Neindorf, Brooke (20 February 2015). Adelaide University researchers have discovered the loss of oyster reefs believed to have disappeared over 70 years ago due to dredging in South Australia ABC News. Retrieved 13 October 2025.
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