Photo by NASA

A massive toxic algal bloom has killed hundreds of marine species across South Australia’s coastline, prompting Premier Peter Malinauskas to declare it a “natural disaster” – the first of its kind in the country’s history.

Unprecedented scale

The harmful algal bloom, dominated by Karenia mikimotoi, has devastated marine ecosystems since March 2025. Spanning over 4,500 square kilometres, the bloom has penetrated 30 metres deep, transforming thriving reefs into barren seascapes.

“We’ve never seen an algal bloom of this size and this scale in the history of our country’s coastline,” Malinauskas said.

Cleanup crews are collecting up to 200 kilograms of dead marine life daily, with over 400 species affected and 15,000+ individual deaths recorded by citizen scientists.

Climate change link

The disaster stems from a marine heatwave that began in September 2024, causing ocean temperatures to soar 2.5°C above normal. Combined with calm seas and nutrient-rich conditions, this created perfect conditions for the toxic algae to flourish.

Marine ecologist Janine Baker described the bloom as “testament to long-term, increasingly evident climate-mediated change in southern Australian waters.”

Economic impact

The bloom has devastated South Australia’s AUD $480 million seafood industry, with Marine Fishers Association reporting “zero life” wherever the bloom hits. About a third of state waters are now completely devoid of fish.

Government response

Both state and federal governments announced a combined AUD $28 million support package for research, cleanup, and industry support. However, unlike bushfires or floods, there is no way to actively combat the bloom.

“With a bushfire, you can put the fire out… whereas this is so entirely unprecedented,” Malinauskas noted.

Paul Gamblin of the Australian Marine Conservation Society called the disaster proof that “nowhere is immune from the accelerating impacts of climate change,” demanding coordinated action matching the emergency’s scale.

The bloom’s future depends entirely on natural weather patterns, with elevated algae levels persisting across much of the coastline despite recent cooling.