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Toxic algal bloom off South Australia

Felix Levesque, Friday March 21, 2025 - 11:53 AEDT

A bloom of toxic algae off South Australia's Fleurieu Peninsula has caused marine life fatalities as well as respiratory symptoms amongst surfers and beachgoers.

South Australia has been stuck under a persistent pattern of light winds and prolonged hot temperatures over the past few weeks. Very warm sea surface temperatures over the region with a marine heatwave allowed the algal blooms to thrive. This can be seen through the bloom of Chlorophyll-A detected on satellite in the image below (the deep red bursts of colour).

Image: Snapshot of Chlorophyll-A concentrations around the South Australian coastline on Friday, March 14. Source: Integrated Marine Observing System

The ongoing stress on the ecosystem, along with the algal bloom, has led to widespread death of marine life over the region. As seen in the pictures below, many creatures are washing up along parts of the Fleurieu Peninsula’s beaches.

Image: a dead weedy sea dragon washed ashore. Source: Andy Smyth @andysmythy / Instagram

Image: a dead fish with brown foam washed ashore. Source: Andy Smyth @andysmythy / Instagram

Surfers and beach goers attempting to get relief from the heat over the weekend reported respiratory problems and sore eyes. Waitpinga and Parsons beaches have reportedly been closed as a result.

Image: a beach closure sign at the popular South Australian beach due to the suspected algal bloom. Source: Andy Smyth @andysmythy / Instagram

Image: Snapshot of Chlorophyll-A concentrations around the South Australian coastline on Wednesday, March 19. Source: Integrated Marine Observing System

The image above shows that chlorophyll-A concentrations remained elevated this week. With high pressure cells forecast to slowly transit over the region in the coming weeks, warm days with little wind will promote further algal blooms. Strong winds and waves are required to stir up this layer, but no powerful cold front is expected in the coming week or two at this stage.

- Weatherzone

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