Our Sea Under a Toxic Blanket: The Algal Bloom Environmental Crisis on the Fleurieu Peninsula

What’s Behind the Bloom?

The microscopic culprit is a toxic algae called Karenia mikimotoi. To the naked eye, it looks like little more than murky water or patches of froth. Yet under the microscope, it’s revealed as a single-celled organism capable of unleashing devastation. Unlike some algae that only cloud the water, this species actively damages marine life—clogging gills, releasing toxins, and depriving animals of oxygen.

But why here, and why now?

This bloom is the result of a “perfect storm” of environmental conditions. Over the past summer, the waters of Gulf St Vincent and the Southern Ocean have been unusually warm—more than two degrees hotter than long-term averages. Prolonged calm weather has left the sea unnaturally still, reducing the mixing of surface and deeper layers. And lingering nutrients, delivered by decaying marine vegetation, Murray River floodwaters and coastal run-off, have acted like fertiliser. Put together, it’s the ideal incubator for algae to multiply on a staggering scale.

The Scale of the Disaster

From Waitpinga and Parsons beaches on the Fleurieu, the bloom spread like an invisible tide. By winter, it had stretched across more than four thousand five-hundred square kilometres—twice the size of the ACT—encompassing Kangaroo Island, Yorke Peninsula, the Coorong north lagoon, Adelaide’s metropolitan coast, and even the Port River dolphin sanctuary.
Sadly, international experts are unable to predict when the bloom may dissipate - it could stay for months to come.

The toll on wildlife has been heartbreaking. Well over 13,000 animals, across nearly 400 species, have been reported dead. On the Fleurieu alone, more than 200 species have been found washed ashore—Port Jackson sharks, stingrays, cuttlefish, crabs, octopus, seadragons, and countless fish. Divers have described scenes of silent devastation: normally vibrant reefs stripped of their colourful inhabitants, and seagrass beds littered with lifeless shells.

It’s not just numbers. It’s the specific creatures that matter. Leafy seadragons, the Fleurieu’s most iconic residents, have been found dead in disturbing numbers. Many were breeding adults—those crucial to sustaining future generations. Southern calamari, famous for their spectacular breeding aggregations, have suffered heavy losses. For slow-reproducing species, even a single lost season can have long-lasting impacts.

Ripple Effects Beyond the Waves

While the algae itself is marine, the damage doesn’t stop at the waterline. Shorebirds and waders rely on the invertebrates of our tidal flats—molluscs, crabs, worms—for food. With so much of that base layer killed or stressed, food chains risk unravelling.

This spring, migratory birds will begin their epic journeys from Siberia, Alaska, and northern Asia back to southern Australia. They will arrive at the Coorong and Fleurieu beaches expecting the rich feeding grounds that have sustained them for millennia. Instead, they may find mudflats and sandy shallows eerily bare. What will happen if they cannot refuel for the final leg of their journey? Ornithologists fear some may fail to complete the migration, or be forced to bypass South Australia entirely.

Human Impacts

Though the primary disaster is ecological, people have not been immune. Swimmers and surfers who entered the water near bloom patches have reported eye irritation, coughing, and sore throats. Families have avoided once-bustling beaches, concerned about safety.

Economically, the blow is already real. Fleurieu businesses dependent on coastal tourism—cafés, surf shops, holiday parks—report declines in bookings and visitor traffic. Commercial fishers face enormous uncertainty, with traditional grounds disrupted or closed. For a region where the sea is woven into everyday life, the costs are felt not just in lost dollars but in community identity.

Will the Sea Heal Itself?

The question on everyone’s lips is whether the bloom will end naturally—and if so, when. Scientists believe the algae will only dissipate once winter storms arrive with enough force to churn the ocean, mixing the surface waters and scattering the bloom. If storms are weak or delayed, the crisis could stretch into next year.

Even if the bloom ends, recovery will not be quick. Some species may bounce back in a season or two, but others—particularly long-lived, slow-breeding creatures—could take decades to recover. Entire local populations of Leafy & Weedy seadragons, cuttlefish, or rays could have been lost. If habitats such as seagrasses meadows or sponge gardens collapse, they may require active human restoration to return.

Government Response

Faced with the scale of the disaster, the South Australian government has mobilised funding for monitoring, clean-up, and support to industries. Community groups, scientists, and volunteers have been crucial in documenting the extent of marine deaths and advising on response priorities.

But what about the federal government? Many South Australians have called for the bloom to be declared a natural disaster, which would unlock additional financial assistance and national coordination. So far, the federal government has declined to do so, arguing that the event, while devastating, doesn’t fit the criteria for traditional disaster declarations used for floods, fires, and storms. Instead, Canberra has committed targeted funding packages in the tens of millions to support science, industry, and community recovery.

This has left many conservationists and local residents frustrated. To them, the distinction between a fire sweeping across farmland and an algal bloom wiping out marine life feels arbitrary. Both leave devastation in their wake, and both demand urgent intervention. The debate has shone a light on how unprepared our disaster frameworks are for ecological crises driven by climate change.

Looking Ahead: A Fragile Future

So what does the future look like for the Fleurieu’s seas?

The honest answer: uncertain. If the bloom disperses this winter, recovery can begin. But with warming seas and shifting weather patterns, there is no guarantee this will be a one-off. Climate models predict more frequent marine heatwaves, longer calm spells, and more nutrient run-off from floods and catchments. In other words, the recipe for harmful algal blooms may become more common.

That means the Fleurieu—and South Australia as a whole—must prepare for a new normal. This includes:

• Long-term monitoring of coastal waters to detect blooms earlier.
• Emergency action plans for species most at risk.
• Active restoration of habitats like seagrasses, oyster reefs, and sponge gardens.
• Policy shifts recognising ecological disasters as legitimate natural disasters, worthy of national support.
• Community involvement, empowering volunteers and local groups to collect data, rescue wildlife, and advocate for stronger climate action.

For communities along the Fleurieu, there are practical steps we can take:

• Report sightings of marine deaths or unusual conditions. These records are vital for scientists tracking the bloom.
• Stay safe by avoiding discoloured water or foam, and following beach closure notices.
• Support local conservation groups working on restoration and advocacy.
• Add our voices to calls for better climate action, so that our children and grandchildren inherit seas rich with life.

Above all, we can bear witness. By recording what’s happening, telling these stories, and refusing to accept the loss as “normal,” we ensure that this disaster is not ignored.

A Turning Point?

The 2025 algal bloom has been catastrophic. It has tested our ecosystems, shaken our communities, and revealed the vulnerability of our seas to climate extremes. Yet it also offers a turning point.

If we treat it as a warning—a vivid signal of how climate change is reshaping our coasts—we may yet respond with the urgency required. By investing in restoration, reforming disaster frameworks, and confronting the warming of our oceans, we can give the Fleurieu’s sea life a fighting chance.

Our region has always been defined by its connection to the sea. Whether through fishing, surfing, diving, or simply walking the beach, the ocean is our shared heritage. It’s worth fighting for—not just to recover from this bloom, but to protect the living richness of our coasts for generations to come.

Keep up to date with regard to the Algal Bloom
South Australian Government
Biodiversity Council

Why You Should Join Biodiversity Victor Harbor?

Biodiversity Victor Harbor is a community-driven, not-for-profit organisation established in 2023.  Incorporated and registered as a Charity, Biodiversity Victor Harbor unites individuals from diverse backgrounds who share a deep commitment to our region's natural environment.
Donations are tax-deductible,

Join today
Simple. Free. No obligations

Image: Joseph C Boone - Own work, CC BY-SA 3.0,