Toxic Waters: Algae Bloom Devastates South Australia
A toxic bloom of Karenia Mikimotoi has been raging since March, driven by a prolonged marine heatwave and unusually calm waters.
LOS ANGELES - According to Green Left Weekly, the affected area now spans 4,400 to 4,500 square kilometers — about the size of Kangaroo Island — stretching from Gulf St. Vincent to the Coorong and metropolitan Adelaide. The Guardian reported that blooms have been observed up to 20 meters deep in some zones.
What is an algal bloom? An algal bloom is a rapid overgrowth of microscopic algae, often caused by warm temperatures, nutrient runoff, and still water. While some blooms are harmless, Karenia Mikimotoi produces reactive oxygen species that damage gills and internal organs in marine life. When the bloom dies off, bacteria depletes oxygen levels in the water, creating hypoxic and anoxic zones therefore triggering additional mass deaths.
What does this all mean? The Guardian reported that more than 12,000 animals from nearly 400 species have died, including sharks, rays, leafy sea dragons, cuttlefish, octopuses and invertebrates.
Underwater footage, obtained by Great Southern Reef Foundation divers near Ardrossan, shows fish swimming through “dark neon green” waters. Wobbegongs and stingrays were also observed in distress.
Algal toxins released during the bloom damage gills, cause internal hemorrhaging and create what marine biologists described to The Guardian as an “underwater bushfire” — a slow-motion ecological disaster unfolding beneath the surface.
Although non-toxic to humans, the algae has caused skin, eye and respiratory irritation among surfers and beachgoers. Reports on TikTok and other platforms show videos of dead marine animals, murky green water and growing concern from coastal communities.
Pet owners have reported to Adelaide Now that their dogs experienced sneezing, bleeding gums and seizures after visiting affected beaches. Officials have urged the public to keep pets out of the water until further notice.
According to ABC News, fisheries and tourism industries are suffering severe losses. Mussel and Pipi harvesting bans remain in effect, and some operators expect next season to be “a complete write-off.”
The exact cause of the bloom is not fully known. However, Thrivability Matters reports that sea temperatures have been 2.5 to 3.2 degrees Celsius warmer than average since September 2024, while calm weather has prevented normal water movement and dispersal. Marine scientists from the South Australian Department for Environment and Water have also cited nutrient runoff from past River Murray floods as a contributing factor.
The government's response has included $14 million AUD in emergency funding for cleanup efforts, financial relief and ecological research, according to Environment Minister Murray Watt, speaking to The Guardian. A matching $14 million AUD was pledged by the South Australian government, bringing the total to $28 million AUD.
Critics, including Greens Senator Sarah Hanson-Young, argue the response came too late. “If this was happening off Bondi Beach, […] I guarantee we would have had a national response weeks ago.”
The event has not yet been formally declared a natural disaster, but pressure is mounting. In an interview with ABC Radio, Minister Watt said, “We’ll continue to work closely with the South Australian government, but the technical threshold for a natural disaster declaration is quite specific.”
