South Australia's Coorong at risk as algae outbreak puts fragile ecosystem on the brink

7NEWS

03-06-2025

The toxic algae bloom that has plagued South Australian coastlines since March has, 'unfortunately,' made its way into one of the state's most fragile ecosystems — the Coorong.
Last week's powerful storm surge was initially welcomed, with hopes it would push cold, salty ocean water onto the shore to disrupt the bloom of the toxic micro-algae karenia mikimotoi algae.
However, those same strong currents instead drove the algae back up the Murray River at Goolwa, entering the Coorong through the Murray Mouth — where the river meets the Southern Ocean.
With ongoing drought conditions and tidal influences, the algae has now found an ideal environment in which it may be impossible to remove.
Previously responsible for murky waters and thick sea foam along the Fleurieu Peninsula, Karenia mikimotoi is also suspected to be linked to the recent deaths of several sharks on Adelaide beaches.
Ecologist and Coorong Environmental Trustee Faith Coleman expressed grave concern about the algae's intrusion into the Coorong's intricate ecosystem.
'Unfortunately, that amazing storm tide managed to push the Karenia straight into the northern lagoon of the Coorong, where it is blooming quite happily,' she said.
'Because of the unique nature of coastal lagoons, once something gets in, it rarely gets out.'
The algae has now established itself in a 'sweet spot' at the end of the northern lagoon, where conditions — including high salinity, warm temperatures, and stagnant water — are perfect for it to thrive. Up to two metres of decomposing marine life, described as 'worm soup,' has already been found, with dead tubeworms and larvae washing ashore.
Experts warn this could disrupt the already delicate food chain in the area.
'Many of the small organisms at the base of the food chain — those vital to shorebirds and fish — are now washing up dead,' Coleman said. 'There isn't anything that lives or grows in the water of the Coorong that is safe from this.'
Local fisherman Glen Hill, owner of Coorong Wild Seafood, said the situation could devastate the region's fishing industry.
'I've bashed my head against the side of the chiller in frustration. I've cried my eyes out,' Hill told 7NEWS.
'If we lose the bottom of the food chain, what do the fish eat?
'Potentially, we could lose everything.'
The storm system also stirred up sediment and, combined with the lack of fresh water, has spiked salinity levels in the Coorong.
This has led to further environmental stress, with fish such as mullet, mulloway, and bony bream suffering visible gill damage — likely caused by the increasingly toxic conditions.
The Department of Primary Industries and Regions (PIRSA) confirmed they are investigating recent fish deaths but have not yet officially linked them to Karenia mikimotoi.
'We continue to work with other relevant government agencies on the current Karenia species algal bloom and associated fish deaths that have been occurring in South Australian waters since March,' a PIRSA spokesperson said in a statement to 7NEWS.
Investigations are underway into reports of a bony bream fish kill in Woods Well Bay and a polychaete worm die-off near Long Point.
Water samples have been collected and results are pending.
'Our role is to investigate any infectious or notifiable animal diseases that may have caused the fish deaths,' PIRSA said.
The Department for Environment and Water (DEW) also confirmed the algae's entry into the Coorong was a known risk — and that any intervention, such as opening the barrages to flush water, could worsen the situation.
'The Coorong is open to the sea via the Murray Mouth and cannot be closed off from the ocean,' a DEW spokesperson said.
'During adverse weather and high tides, SA Water operates the barrages to minimise seawater entering Lake Alexandrina and to limit salinity impacts from reverse flows.'
They added that although the tide pushed the algae in, the Coorong's natural connection to the Murray Mouth meant this could not be prevented.
'Pushing more water through the barrages to try to flush out the algae is unlikely to be effective and could risk spreading the bloom further south,' the spokesperson said.
DEW confirmed it will continue monitoring the Coorong's northern lagoon and reaffirmed the State Government's commitment to protecting the area's ecological health.
In the meantime, PIRSA and SA Health have advised the public not to collect or eat any dead or dying fish or marine organisms found along the shore.
To report unusual sightings of fish kills or affected marine life, residents are urged to contact FISHWATCH on 1800 065 522. Concerns about water quality can be reported to the EPA at 1800 623 445 or by emailing [e-mail].