Toxic Algae Bloom Off South Australia Declared Natural Disaster Amid Mass Marine Deaths

A massive toxic algae bloom off South Australia has killed thousands of marine animals and disrupted tourism and seafood industries. Declared a “natural disaster” by the state, the 4,500 sq km outbreak triggered a joint A$28 million response for cleanup and support. Rising ocean temperatures have worsened the crisis.

A vast toxic algal bloom off South Australia’s coast has been officially labelled a “natural disaster” by State Premier Peter Malinauskas, following extensive damage to marine life and disruptions to the tourism and seafood sectors. Spanning 4,500 square kilometres, the bloom has killed or affected over 400 marine species since it was first detected in March 2025.

The outbreak, driven by the rapid growth of Karenia mikimotoi algae, has intensified due to prolonged marine heatwaves, with ocean temperatures rising about 2.5°C above normal since 2024. The algae attacks fish gills and depletes oxygen as it decays, creating hostile underwater conditions. Over 13,850 dead marine animals, including sharks, rays, and invertebrates, have already been reported by the public through citizen science platforms like iNaturalist.

Premier Malinauskas described the event as an ecological crisis and announced a A$14 million state support package to combat its impact. This will be matched by the federal government, bringing the total to A$28 million. The funding will go towards cleanup operations, marine research, and emergency support for affected businesses, particularly in the fishing and aquaculture industries. Oyster and mussel farms have been temporarily shut due to waterborne toxins.

Tourism operators have also faced severe losses, as beach closures and dead marine animals along the coast have deterred visitors. While Federal Environment Minister Murray Watt acknowledged the severity of the bloom, he refrained from classifying it as a national disaster, which would unlock broader federal aid.

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As environmental experts warn of worsening marine heatwaves in the coming years, concerns grow about Australia’s readiness to handle climate-driven natural events. For now, the focus remains on restoring the damaged ecosystem and stabilising the economic impact on coastal communities.