Everything you need to know about Algal Bloom

• The SA bloom qualifies as a harmful algal bloom (HAB) — a rapid increase of microscopic algae in ocean water.

• The dominant algae detected is Karenia species (particularly Karenia mikimotoi), known to affect marine life through oxygen depletion and physical stress, rather than producing severe human toxins.

Scientists attribute the bloom to multiple interacting factors, including:

• A marine heatwave off SA’s coast, which provided warm, calm conditions favourable for algae growth. 

• High nutrient input from storm events and coastal currents

• Low winds and stable ocean surface layers that allowed algae populations to accumulate.

The bloom first appeared on the Fleurieu Peninsula and has spread into Spencer Gulf, Gulf St Vincent, Kangaroo Island waters, the Coorong and metropolitan Adelaide waterways.

• Metropolitan Adelaide beaches — testing shows declining levels, but areas like Henley Beach still report elevated algae counts.

• Yorke Peninsula coastal waters — ongoing hotspots with still-green water observed and marine life distress reported.

• Port River & West Lakes — HAB detected, monitored by authorities. 

Coorong North Lagoon & Spencer Gulf — presence confirmed via weekly water testing.

• Bloom activity peaked during late summer and autumn 2025.

• It persisted through winter and remains detectable in early 2026, with authorities warning it may return seasonally or emerge again under favourable conditions. 

The bloom has caused mass deaths of stingrays, fish and other species struggling in oxygen-depleted water. 

Citizen science and official reporting documented thousands of marine mortality observations across fish, invertebrates and seabirds.

• Experts warn that repeated or prolonged blooms can harm key fish stocks and marine habitats, potentially disrupting ecological balance. 

There are concerns about ecosystem vulnerability if blooms become more frequent due to climate variability.

• People exposed to affected waters or sea spray report symptoms like coughing, sore eyes and skin irritation.

• Local councils have called for GPs to ask about recent beach visits to better track health links. 

SA Health says no hospitalisations directly linked to the bloom have been reported, and beach visits remain generally safe if discoloured or foamy water is avoided. 

Residents have described persistent smell, reduced beach enjoyment, and stress related to ongoing algal presence. Community surveys reflect mental and physical health concerns. 

• Some oyster and pipi harvesting areas were closed for precautionary reasons due to algal contamination.

The government has implemented fishing fee relief, grants and assistance programs to help commercial operators recover. 

The bloom has negatively impacted tourism, especially in regional areas where visible algal water and marine deaths deter visitors.
Grants and cashback vouchers have been introduced to encourage visitation and support local hospitality businesses. 

The South Australian government launched a $102.5 million Summer Plan that includes:

• Grants and financial support for impacted coastal communities and industries. 

• Infrastructure upgrades at beaches, fishing and aquaculture support, and promotional assistance.

Authorities conduct weekly water sampling across multiple sites in SA, including rivers and coastal jetties, to track algal cell counts and bloom distribution.
Citizen science contributions have also been vital to tracking marine mortality and algal spread. 

Scientists warn that if conditions remain conducive, the algal bloom could persist seasonally or reappear in future years.
Worst-case modelling presented to Parliament even suggests a possibility of decadal recurrence cycles, depending on climate and marine conditions.

Efforts continue to focus on ecosystem resilience, community support, research and monitoring, while balancing human use of coastal resources with environmental health.