SA harmful algal bloom update

04 June 2025

A naturally occurring, harmful algal bloom is affecting parts of the South Australian coastline.

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

What is the latest situation with the harmful algal bloom?

Testing of water in the Coorong North Lagoon has confirmed the presence of the Karenia strain of algae, which has affected parts of South Australia’s coastline.

The testing, which was conducted by the Department for Environment and Water (DEW) and Department of Primary Industries and Regions (PIRSA), shows the algae is present in the Coorong North Lagoon 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. Further testing will be undertaken to determine the specific Karenia strain.

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.

Latest statewide observations show sea surface temperatures are decreasing in shallow coastal and gulf waters due to seasonal cooling and the passing of the cold front.

However, moderate marine heatwave conditions continue across most of South Australia’s coastal regions.

Latest satellite images indicate strong winds linked to the May 26 storm have started to move the algal bloom eastward.

The satellite images monitor the level of chlorophyll-a in the sea, which provides an indicator of algae concentrations, but not necessarily concentrations of harmful algae.

Chlorophyll-a concentrations have decreased along the southern tip and foot of Yorke Peninsula, along the west coast of Kangaroo Island and along the western side of Gulf St Vincent.

Increases in chlorophyll-a have been observed off the southeastern tip and in patches along eastern side of the Fleurieu Peninsula, the upper eastern side of Gulf St Vincent, and along the lower western side of Spencer Gulf.

FISHWATCH has received an increase in reports of fish kills since May 26 as the storm likely picked up fish that were already dead and washed them to shore.

What are the effects of the algal bloom?

The Karenia mikimotoi algal bloom has caused discoloured water and foam along parts of Fleurieu Peninsula, Kangaroo Island and the southern coast of Yorke Peninsula. It has affected various marine wildlife, including fish, sharks, rays, seahorses and other species with gills.

Why has it appeared?

Experts believe there are three 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.

This one is expected to persist until strong westerly winds arrive, which historically happens at the end of April.

However, persistent high pressure systems have delayed these winds.

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.

Swallowing water affected by the algal bloom can cause gastrointestinal symptoms, including vomiting, diarrhoea and abdominal cramps.

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.

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.

Commercial pipi harvesting was closed on 16 April from the Murray Mouth to 10km south of the mouth, to prevent packaging of dead or dying pipis.

Further closures were implemented on 19 May at American River, Port Vincent and Stansbury oyster harvesting areas.

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

What is being done about the bloom?

Government agencies, including the Department for Environment and Water (DEW), the Environment Protection Authority (EPA), the Department of Primary Industries and Regions (PIRSA) and SA Health are monitoring the situation.

Signs are in place at public entry points to affected beaches, and National Parks beaches remain open.

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

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.