Prolonged Toxic Algal Bloom Impacts South Australia: A Year of Environmental, Health, and Economic Disruptions
A significant and prolonged toxic algal bloom, identified as Karenia cristata, has continued along sections of the South Australian coastline for over a year, impacting approximately 20,000 square kilometers. This unprecedented event has been linked to extensive marine life mortality, reported human health concerns, and substantial economic disruption to the state's fisheries. The government's handling of public health advice, particularly regarding the detection of brevetoxins, has drawn scrutiny and calls for greater transparency.
Overview of the Algal Bloom
The current algal bloom is considered one of the largest recorded in Australia's history, predominantly involving Karenia cristata among multiple Karenia dinoflagellate species. Water samples have consistently shown Karenia levels exceeding 1 million cells per liter, significantly above the elevated threshold of 10,000 cells per liter.
DNA analysis of archived seawater samples suggests Karenia cristata was present near Kangaroo Island as early as 2016. However, a dramatic increase in its abundance was observed in 2025, leading to the current widespread bloom. Affected areas include the Yorke Peninsula, Kangaroo Island, Gulf St Vincent, Spencer Gulf, and metropolitan Adelaide.
Impact on Marine Ecosystems
The bloom has contributed to mass mortality events across the marine ecosystem, affecting millions of organisms and over 780 species. Marine life fatalities include iconic species such as weedy and leafy sea dragons, puffer fish, leather jackets, crabs, snails, dolphins, fiddler rays, flathead, sharks, and stingrays. Shellfish and even white sharks have also been impacted.
Leafy sea dragons, which are unique to southern Australia and concentrated in affected areas, have experienced significant population declines, prompting the International Union for the Conservation of Nature to reassess their extinction risk.
Marine environments have sustained widespread damage. Artificial reefs formed by jetties have been affected, while vital seagrass meadows and razorfish populations have been severely impacted or eradicated. Port Jackson sharks have largely disappeared from Adelaide's coast. Disturbingly, an autopsy on a great white shark found on May 5 revealed brevetoxins on its gills.
Human Health Concerns
Exposure to the bloom has been linked to various human health effects. Individuals have reported symptoms including eye irritation, throat discomfort, persistent coughs, respiratory irritation, scratchy throats, headaches, and breathing difficulties.
A study indicated that two-thirds of South Australians reported preoccupation with the bloom, with approximately one-third attributing distress to observing dead marine species. Recreational activities such as swimming, surfing, diving, and beach walking reportedly decreased among 47% of respondents.
Brevetoxins, a compound previously unrecorded in Australia, were detected in several instances. They were found in oysters from three Yorke Peninsula regions in early May, leading to the immediate closure of these areas. Brevetoxins were also identified in the gills of the great white shark found on May 5. Later, in late June, brevetoxins were detected in the organs of two kangaroos, which had been put down in March near where surfers initially reported symptoms. Over 100 kangaroos were culled due to illness.
Economic Consequences
The state’s fisheries and seafood industry have faced substantial challenges due to the bloom. Commercial fishing in Gulf St Vincent and Kangaroo Island has been halted until June 30, 2026. This extended closure impacts key species such as calamari, garfish, King George whiting, western king prawn, and blue swimmer crab. Recreational catch limits have also been reduced in these areas and introduced in Spencer Gulf.
Scientific Investigation
Professor Shauna Murray from the University of Technology Sydney confirmed the identification of Karenia cristata in water samples. Researchers are actively investigating the precise cause of the dramatic surge in the bloom's abundance observed in 2025.
The state's environment department is conducting extensive surveys across over 200 sites to assess the full scope of the bloom's impact on marine ecosystems. A collaborative "Bloomin’ Algae research project" is underway, engaging both citizen and professional scientists to gather crucial data.
Government Response and Health Advice Controversy
The South Australian government reportedly delayed updating its public health advice concerning brevetoxin detection for four months. Initial public statements from Premier Peter Malinauskas and Chief Public Health Officer Nicola Spurrier indicated minimal risk to human health. They characterized symptoms as an "irritant" and stated that brevetoxin was "not a problem" in South Australia.
Despite repeated findings of brevetoxins in May and June, the state's health advice was not updated until early September. The updated advice, announced by a government marine scientist, recommended that asthmatics carry Ventolin at the beach. Premier Malinauskas initially stated the bloom was "not toxic" but later acknowledged brevetoxin's inherent toxicity, while emphasizing the need to inform the public without causing undue fear, likening it to substances like alcohol.
Chief Public Health Officer Professor Spurrier reportedly requested that scientists modify their research paper on the bloom, suggesting references to "severe human health effects" be replaced with "acute and self-limiting human health effects," stating the paper did not reflect evidence observed in SA. Premier Malinauskas stated that no individuals had presented to public hospitals with significant illnesses related to the algal bloom.
Differing Perspectives and Calls for Transparency
Experts, including Professor Shauna Murray and Barbara Kirkpatrick, who studies Florida's algal blooms, have stated unequivocally that the bloom is toxic and the discovery of brevetoxins in Australia was significant.
The opposition and The Greens have called for greater transparency regarding the government's decisions on public health information. Opposition Leader Ashton Hurn stated that the Premier avoided using the word "toxic." Greens SA leader Robert Simms called for the release of the full chain of advice provided to cabinet. Premier Malinauskas has defended the public health decision-makers as a "nation-leading public health team."
Ongoing Concerns
Experts express significant concern that the bloom continues to persist. While urban sites have shown low levels of Karenia in recent weeks, the bloom remains active along the south-west coast of the Yorke Peninsula. This raises particular concerns for the globally unique population of giant cuttlefish that gathers in Spencer Gulf, as cephalopods are often among the first species impacted by such blooms. The potential for the bloom to recur under suitable seasonal conditions is also a significant ongoing worry.