The South Australian coast is currently witnessing the largest and most destructive algal bloom in the country’s history, persisting for a year and spreading over more than 20,000 square kilometers.

Environmental surveys across multiple sites are ongoing, with results anticipated in June, as scientists monitor the bloom’s persistence and its ongoing threat to biodiversity and ecosystem recovery.

The bloom has delivered profound psychosocial and economic blows to communities, triggering sustained distress, reduced participation in recreation, and near-collapse of the state’s fisheries and seafood sector due to fishing restrictions and stock declines.

Experts warn the bloom could persist under favorable conditions, raising concerns about repeated or extended events and additional risk to marine life, including giant cuttlefish populations in Spencer Gulf.

Habitat degradation is widespread, with seagrass meadows and razorfish habitats severely affected and Port Jackson sharks largely absent from Adelaide’s coastline.

Extensive marine wildlife mortality has occurred, impacting more than 780 species and devastating iconic creatures like the leafy sea dragon, whose populations have collapsed in affected areas.

The bloom is caused by Karenia cristata, a rare and highly toxic algae species identified in South Australia’s waters, with only two other global records besides Australia.

DNA analysis shows Karenia cristata was present in archived samples for nearly a decade before the surge in 2025, as researchers explore triggers and the potential for similar events elsewhere.