SA harmful algal bloom update

16 July 2025

A naturally occurring, harmful algal bloom is affecting parts of South Australia's coastline.

Wide photo of Parsons Beach on the Fleurieu Peninsula — Parsons Beach.

What is the latest situation with the harmful algal bloom?

South Australia’s flagship fisheries patrol vessel Southern Ranger will conduct underwater observations of the harmful algal bloom in the Gulf St Vincent to understand the effect on the ecosystem.

Numerous locations will be visually surveyed with remote operated vehicles and this information will help authorities to better understand the rate of potential recovery once the bloom dissipates.

Marine sanctuaries, where an extensive data set already exists, will be surveyed to provide a comparison with the observations from the trip.

The harmful algal bloom affecting South Australia’s coastline has been detected in the Port River.

Testing has confirmed elevated levels of the Karenia species along the metropolitan coastline, and very high levels at the Garden Island and Outer Harbor boat ramps.

This is the same species of algae first detected on the Fleurieu Peninsula in March.

State government agencies are taking weekly water samples at 17 sites across West Lakes, the Port River, the Patawalonga River and the end of four jetties at Largs Bay, Grange, Glenelg and Port Noarlunga.

The Port River is home to the Adelaide Dolphin Sanctuary, whose dolphins and their water quality are monitored regularly by National Parks and Wildlife Service (NPWS), and Flinders University in collaboration with the Environment Protection Authority.

Dolphins in the sanctuary are not believed to be at immediate risk but NPWS is investigating potential risks by monitoring water quality and undertaking algae testing.

Latest statewide observations show sea surface temperatures have continued to decrease in shallow coastal and gulf waters.

However, deeper continental shelf waters, including around Kangaroo Island and southern Yorke Peninsula, continue to experience moderate to strong marine heatwave conditions of 1-2C above average.

Satellite imagery of chlorophyll-a, which provide an indicator of algae concentrations but not necessarily concentrations of harmful algae, show increased levels across most of Gulf St Vincent.

These elevated levels have been recorded across the gulf as far south-west as Edithburgh on Yorke Peninsula to Aldinga in the east.

Other regions include areas along the upper Spencer Gulf, the north coast of Kangaroo Island, smaller patches around the Fleurieu Peninsula and in the Coorong.

There have been multiple reports of fish deaths along the metropolitan coastline – North Haven between the river mouth and marina breakwater, Tennyson Beach, north of Grange jetty and south of Christies Beach Surf Life Saving Club – and Port Broughton after the June 24 storm.

Testing of water in the Coorong North Lagoon has confirmed the presence of Karenia between Seven Mile Basin and Long Point.

Experts believe the algae flowed through the Murray Mouth and into the lagoon during a strong cold front, including a storm on May 26 and high tide on May 27.

Weekly testing of the Coorong will be undertaken to analyse the algal bloom's movement. The Coorong region remains open and visitors are advised to check signage and avoid contact with discoloured water, foamy water, or water where marine life is dead or in poor health.

What are the effects of the algal bloom?

The algal bloom has caused discoloured water and foam along parts of South Australia's coastline. Karenia mikimotoi does not cause long-term harmful effects in humans but has affected various marine wildlife, including fish, sharks, rays, and a wide range of invertebrates.

Why has it appeared?

Experts believe there are three potential plausible contributing factors causing the bloom, which started in March:

A marine heatwave that started in September 2024 – with sea temperatures about 2.5°C warmer than usual – combined with calm conditions, light winds and small swells.
The 2022-23 River Murray flood washing extra nutrients into the sea.
An unprecedented cold-water upwelling in summer 2023-24 that has brought nutrient-rich water to the surface.

The last large event of this type of algae recorded in SA was at Coffin Bay in 2014.

How long might the bloom last?

Similar blooms around the world have lasted from a week to several months, depending on wind, rain and ocean temperatures.

Nothing can be done naturally to dilute or dissipate the bloom.

Is the bloom harmful to people?

Karenia mikimotoi does not cause long-term harmful effects in humans.

However, exposure to discoloured or foamy water can cause short-term skin or eye irritation and respiratory symptoms, including coughing or shortness of breath.

These symptoms usually resolve within several hours of leaving the beach.

What should I do if I experience symptoms?

If you are outdoors and experience irritation, go indoors, close windows and rinse exposed skin.

If symptoms are more severe or do not resolve, seek medical advice from a GP and call 000 if it is a medical emergency.

Can I swim or walk on the beach?

Avoid swimming or surfing in discoloured water, foam or where marine life is dead or in poor health.

If you experience irritation, go indoors, close windows and rinse exposed skin, seek medical advice if symptoms persist or call 000 in an emergency.

Do not touch or eat dead or dying fish, shellfish or marine wildlife. Fish caught alive are safe to eat.

Follow beach signage and directions from NPWS rangers.

What should I do if I'm walking my dog on the beach?

Dog owners should keep their pets under effective control to prevent them eating dead or dying fish, which may cause illness.

Do not let your dog swim in discoloured water and foam, or where marine life is dead or in poor health.

Is it safe to eat seafood from affected areas?

Do not eat dead or dying fish, cockles or other marine life found on the beach. Fish caught live are safe to eat.

Report fish deaths to FISHWATCH on 1800 065 522.

Oyster harvesting areas are temporarily closed at American River, Port Vincent, Coobowie and Stanbury.

Commercial pipi harvesting is temporarily closed from the Murray Mouth to 10km south of the mouth.

A precautionary closure was enacted on July 9 at Boston Bay, Bickers Island, Lower Eyre and Proper Bay harvesting areas after brevetoxins (neurotoxic shellfish poisons) were detected.

Ongoing testing in open harvest areas continues to ensure product safety standards are upheld.

What is being done about the bloom?

The state government has established an algal bloom taskforce and reference group to help industries and stakeholders respond to and recover from the algal bloom affecting South Australia’s environment and coastline.

The Harmful Algal Bloom Reference Group, which comprises representatives from Seafood Industry South Australia, RecFish SA, Conservation Council, Tourism Industry Council and First Nations groups will:

Represent sectors to identify key issues for government to consider in managing and recovering from the algal bloom.
Identify opportunities to further engage with and provide more information to industry sectors, stakeholders and the community
Provide ideas for government consideration to support an expanded scientific monitoring program.

Agencies, including the Department for Environment and Water (DEW), Department of Primary Industries and Regions (PIRSA), Environment Protection Authority (EPA) and SA Health, met with commercial fishers, tourism operators and local councils at a forum on July 4.

The meeting was held to provide an update, including ongoing public health information and environmental effects, and address future research priorities associated with the algal bloom to better understand how to mitigate future outbreaks.

What are the potential effects of the bloom on marine parks?

DEW, SARDI and Fisheries SA are conducting preliminary scoping surveys to assess the effects of the algal bloom on Gulf St Vincent, including marine parks.

This will inform the extent of effect and help determine more detailed assessments.

Is quarry sand contributing to the bloom?

Quarry sand is tested to meet strict environmental standards to ensure it is compatible with existing sand on the beach.

As the algal bloom is naturally occurring, there is no link between it and the delivery of external quarry sand to West Beach and Henley Beach.

Are desalination plants contributing to the bloom?

No health issues are known to be associated with brine discharged from desalination plants and brine is not linked to increased algal growth.

All marine desalination plants operated by SA Water are regulated by the Environment Protection Authority, which ensures appropriate management of brine outflow.