Dead fish and other marine life in the tens of thousands have washed up on South Australian beaches and there have been multiple reports of people suffering respiratory problems after being exposed to sea spray.

The cause is an invasion of a harmful algal bloom (HAB) identified as Karenia mikimotoi that has been decimating marine life, shutting down fisheries and aquaculture, and affecting access to SA’s beaches for several months.

According to marine ecologist Dr Dominic McAfee, SA’s current event is akin to an underwater “bushfire”.

Dr McAfee told IA:

“The scale of this is unmitigated devastation. It’s burning down and destroying underwater forests and marine ecosystems. And we need a response that's similar to how we respond to bushfires on land.”

While algal blooms occur naturally in waterways, when environmental conditions allow, excessive toxin-producing events known as HABs occur, which damage the environment by depleting oxygen in the water, leading to large-scale fish and animal deaths. 

South Australia’s harmful algal bloom has been detected at Adelaide’s West Lakes and Port River, the Spencer Gulf, Kangaroo Island, the Coorong's North Lagoon and along the coastline from Victor Harbor to Robe. 

Harmful algal blooms are worsening due to ocean warming, marine heatwaves and nutrient pollution. They have occurred around the world, from Botswana (where 350 elephants died after drinking affected water) to Mexico and the Arctic Circle, and can even create what are known as “dead zones”, which cannot support any life, such as in the Baltic Sea, where more than 70,000 square kilometres are affected.

Disturbingly, HABs have also been linked to several degenerative diseases.

IA understands that many people, including Dr McAfee and IA’s Mark David and their colleagues and friends, have experienced sore eyes and throats and respiratory problems.

In Victor Harbor, the effects of the bloom even forced the temporary closure of the Victor Harbor Horse Drawn Tram with the following announcement:

Due to the Algae Bloom the tram will be shut until further notice. Please note that this is precautionary, whilst we await further information from official sources.

The safety of our horses and staff is paramount.

According to South Australian health authorities, this bloom is considered non-toxic to humans – providing you don’t consume dead fish – but exposure can cause temporary skin, eye and lung irritation.

However, it’s important to note that although not a lot is known about their long-term health effects, exposure to such blooms has been linked to increased incidences of several neurodegenerative diseases, including motor neurone disease (MND).

This is due to a toxin known as BMAA (β-Methylamino-L-alanine), which has been detected in previous algal blooms in Australia.

The question of whether BMAA is present in SA’s current harmful bloom and whether or not authorities are testing for its presence was put to the SA Department of Primary Industries and Regions (PIRSA), and IA received the following *emailed response:

PIRSA has been advised by SA Health that scientific evidence does not support a causal link between BMAA and neurodegenerative diseases.

Testing for BMAA is not warranted and is not included in water sampling related to the algal bloom.

IA spoke with PIRSA CEO Professor Mehdi Doroudi, who explained that a special task force has been set up to monitor and address the harmful algal bloom:

“We have been tracking the bloom since March and we will now be investigating further, increasing underwater observations to better understand potential impacts on the ecosystem.”

The SA Government has established a dedicated task force and provided monetary support to affected industries. It has also increased its investigative resources, including focusing the Integrated Marine Observing System (IMOS) in ecologically important areas.

Given algal blooms can be triggered by excessive nutrients, IA asked if any plans are underway to reduce nutrient loads from agricultural run-off, sewerage and stormwater discharge.

Professor Doroudi said there are no immediate plans to change these:

Discharges are closely monitored and have been unchanged for many years.

Affected areas have been significantly impacted by unprecedented 2.5 to 3-degree higher ocean temperatures in South Australian waters.

This, as well as cold water upswells from recent floods and now, drought conditions with extended periods of sunshine, have all combined to create an environment for these micro-organisms to bloom.

Professor Doroudi added:

We will be collecting more data to better understand potential impacts.

We are also working with the Federal Government, CSIRO and other agencies and colleagues around the country, and we are in the process of connecting with UNESCO and FAO as well, to learn and share available information and how best to utilise it in the decision making process.

Greens Senator for South Australia Sarah Hanson-Young has urged Prime Minister Albanese to declare a national disaster and devote significant national resources to deal with the extreme event.

Senator Hanson-Young said:

If there were dead fish washing up on Bondi Beach every day, there would be a national outcry and response.

South Australians deserve the same support from our Federal Government that East Coast states would demand.

Dr McAfee says:

This is an unprecedented event on a massive scale and it's essential that we get eyes under the water, because what we're seeing on the surface and on our beaches is likely just the tip of the iceberg.

We need more investment in systematic marine monitoring on a far greater scale.
 

And more research capacity to collect extensive data in order to develop greater predictive tools, particularly as climate change will continue to manifest these disasters.

As environmental activist Paul Watson warned, “If the oceans die, we die".

EDITOR"S NOTE:
*This response from PIRSA was received subsequent to publication on 18 July 2025.

For public health advice in South Australia, visit: Water quality alerts | SA Health.
For regular algal bloom updates, visit: Department for Environment and Water – SA harmful algal bloom update.

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