The South Australian government has intensified surveillance along parts of its coastline as a resurgence of toxic algal bloom activity raises fresh environmental and public health concerns, even as scientists report early signs that the outbreak may be losing strength.
The monitoring effort is being led by the South Australian Research and Development Institute, which has identified two key hotspots requiring ongoing attention: the Yorke Peninsula and Kangaroo Island. Researchers say the bloom, dominated by the toxic algae Karenia, has fluctuated in intensity over recent weeks, prompting both caution and guarded optimism.
SARDI executive director Mike Steer said authorities were committed to maintaining continuous monitoring through the warmer months, when conditions are most favourable for harmful algal growth.
“It’s important that we maintain monitoring and surveillance through summer and into autumn to make sure that we’re on top of it,” Steer said on Wednesday. “If you compare the data now to where we were a few months ago, it has significantly reduced, which is some form of positive. But we just need to be careful in our interpretation.”
According to Steer, the bloom has been particularly active in recent weeks around the south-western end of the Yorke Peninsula, including waters adjacent to Innes National Park. The affected stretch extends from Chinamans Hat Island through to Browns Beach and around Corny Point.
While activity in this region has increased spatially, Steer noted that the actual concentration of algal cells has been declining, a trend scientists see as encouraging.
“The concentration of those cells is reducing, which is good to see,” he said, adding that reductions in cell density can lessen the severity of ecological impacts even if the bloom remains visible.
On Kangaroo Island, researchers are tracking the westward movement of the bloom, particularly north of the island around Stokes Bay. Here too, Steer said, the overall intensity appears to be diminishing.
Despite the apparent easing, authorities are warning coastal communities to expect continued environmental fallout. Foaming events and dead fish are likely to keep appearing along beaches on both Kangaroo Island and the Yorke Peninsula for some time.
“We will see dead fish, particularly any gill-breathing organism, are negatively impacted by the algal bloom,” Steer explained. “When the algae dies, it decomposes and draws oxygen out of the water. That lack of oxygen is what leads to fish kills and wash-ups in impacted areas.”
Foam accumulation, often one of the most visible and distressing signs of a bloom, is expected to be especially pronounced along the Yorke Peninsula coastline.
“It’s a high wave-energy area,” Steer said. “When you combine that with onshore winds, you get churning organic material — the algal species plus a whole heap of other naturally occurring matter — and that washes ashore as foam.”
Health authorities have reiterated advice urging people to avoid swimming or surfing in areas where water appears discoloured or excessively foamy, particularly those prone to skin or respiratory irritation. While toxic Karenia species can pose health risks, Steer stressed that not all irritation experienced in the ocean is linked directly to harmful algae.
“In areas where there’s no Karenia or only low or natural levels, there’s a lot of other things in the water that can create itchy skin,” he said. “Being a surfer myself, sometimes you come out feeling crusty from saltwater, or there might be bluebottles around.”
Addressing public speculation that offshore dredging or other coastal development may have triggered the bloom, Steer said the evidence pointed instead to large-scale environmental drivers.
“We’re looking at significant ecosystem events like the record-breaking Murray River flood, system-wide upwelling seasons along the coast, and an unprecedented marine heatwave that we haven’t experienced for more than 40 years,” he said. “These are really big drivers that are most likely operating collectively. Small, localised activities along the coast would have a negligible impact, if any at all.”
Latest water testing results from the week beginning December 28 offer further reassurance for metropolitan areas. Of 21 onshore testing sites around Adelaide, 20 recorded no or low levels of Karenia.
In regional South Australia, results were similarly encouraging, with zero or low levels detected across much of the Eyre Peninsula, Yorke Peninsula and Fleurieu Peninsula. However, elevated concentrations were found at Whyalla Jetty, where counts reached 14,000 cells per litre, and at Emu Bay Jetty on Kangaroo Island, which recorded 27,820 cells per litre.
Scientists say continued vigilance will be crucial in the weeks ahead, as summer conditions persist and weather patterns evolve. While the bloom may be weakening, Steer cautioned that harmful algal events are complex and can change rapidly, underscoring the need for sustained monitoring and public awareness along South Australia’s diverse and environmentally sensitive coastline.
