“Nothing can be done” to dilute or dissipate an algae bloom that is devastating marine life across formerly pristine South Australian coastlines, the state’s residents and hard-hit fishing industry are being told by the Department of Environment and Water.

Three contributing causes have now been identified for the bloom which has been choking large parts of South Australia’s coast for more than three months, as authorities scramble to maintain confidence in their handling of what is being called an “environmental catastrophe”.

Federal Minister for the Environment Murray Watt on Monday promised $14 million to deal with the algae event, but did not specifically mention if it was one-off disaster funding.

Know the news with the 7NEWS app: Download today

“It’s obviously a very distressing event for all South Australians and, I think, the whole country,” he said.

“There’s no doubting whatsoever that this is a very serious environmental event facing South Australia.”

The funding is expected to be spent on beach clean-ups across SA coastlines, scientific research, business assistance, communication and planning to mitigate future blooms.

The combined effects of river floods, a cold water upswell and now warmer than average water temperatures — which have created the conditions in which the algae thrives — are not easily combated, the South Australian government’s Department for Environment and Water (DEW) has said.

Since March when surfers first began falling sick after riding the waves at Goolwa on the Fleurieu Peninsula, the toxic karenia mikimotoi algae has spread along the coastline to Adelaide and around the otherside of the Yorke Peninsula, like Port Broughton — about 250km north of where it was first detected.

The algae bloom — now estimated to be about 4,500sqkm in size — has killed thousands of fish and other marine life, with regular reports of rotten carcasses washing up on beaches.

DEW said nutrients washed downstream during the River Murray floods and deep-sea nutrients pushed into shallow waters during a cold water upswell have caused a mass feeding ground rich in nitrate and other micro-plankton — meaning there is plenty of food for all sorts of marine life, including various algae species.

These factors alone would normally mean a nutrient-rich season for ocean-based primary producers such as fishermen and oyster and muscle farmers.

But they were soon followed by warmer than average water temperatures causing conditions perfect for the algae to develop faster and overwhelm other marine life, with the micro-plankton karenia mikimotoi outbreak quickly taking root — and both eating up the other micro-plankton other species rely on, while being consumed spreading its toxins that can kill other forms of sea life and make humans sick.

South Australia’s struggling seafood industry is still holding its breath for the bloom to dissipate, while residents and visitors to the area have been advised to avoid swimming at algae-affected beaches.

Local fisherman and Coorong Wild Seafood owner Glen Hil 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.”

And it’s having a knock-on effect across the wider industry, with reports seafood sales are plummeting as consumers question where the produce has come from, while several oyster and muscle-producing sites have been shut down.

It’s not the first time South Australia has had to contend with a karenia mikimotoi outbreak, with a previous bloom recorded in Coffin Bay in 2014 according to DEW.

Karenia mikimotoi can be found worldwide, including Northern America, with many types of harmful algae blooms becoming more frequent due to climate change.

Coorong Environmental Trust co-founder Faith Coleman has told 7NEWS: “Human beings are part of our ecosystems but if we get the balance wrong in the environment all of it will fall over.

“And so, when there are community members who are distressed and we are seeing really clear signatures of climate change … it’s important that we get onto it very, very quickly.”

Marine heatwave

While South Australia was dealing with a drought, the ocean was also being affected by the weather with “sea temperatures about 2.5C warmer than usual combined with calm conditions, light winds and small swells,” according to SA Water.

In Australia, often warmer waters on the eastern coast can be seen as colour bleaching on coral reefs.

But according to the Australian Research Council (ARC), the impact of m arine heatwaves can also include “harmful algal blooms, coral bleaching and organism mortalities”.

ARC said marine heatwaves can occur in any ocean region and during any season.

But what exactly causes a marine heatwave? ARC said there are key factors that may trigger a marine heatwave, with the “atmospheric” issues such as sunlight being a big factor — when there is minimal cloud cover, the ocean water warms up more.

Wind also plays a factor in cooling the water surface so with less wind the water stays warmer.

According to the Bureau of Meteorology (BOM), sea surface temperatures (SST) around Australia during May 2025 were 0.62C above the 1991–2020 average, making it the warmest May on record since observations began in 1900.

Since July 2024, SSTs have been the warmest or second warmest on record for each respective month.

River Murray floods

Unprecedented flooding on the Australian east coast caused a massive knock-on effect, not only for those at the top of the Murray Darling Basin but at the bottom in South Australia.

On the average day, 15 gigalitres of water — or 6000 Olympic-sized swimming pools — is expected to pass through monitoring stations in SA’s Riverland region.

However, as the Murray Darling Basin flooded, a peak of 186 gigalitres — or 74,400 Olympic-sized swimming pools — was pouring into the River Murray daily and countless acres of farmland, homes and shacks were inundated by the “once in a generation” flooding event.

SA Water has acknowledged the flooding did flush “nutrients” into the Murray mouth and surrounding beaches.

Beaches around where the Murray meets the ocean mouth turned brown for months, with farm machinery brought in to clear a massive fish kill as tons of immature carp were flushed out to sea.

Unprecedented cold-water upwelling

Upwelling is an oceanographic phenomenon that involves wind-driven motion of dense, cooler, and usually nutrient-rich water from deep water towards the ocean surface, according to Jochen Kaempf, an Associate Professor of Natural Sciences (Oceanography) at Flinders University.

Sunlight does not reach far into the sea, so the upwelling ensures that microscopic phytoplankton — single-celled organisms that depend on photosynthesis to thrive, are able so do so as the currents of the water bring them to shallower waters.

It usually is celebrated by fishing industries as phytoplankton attracts deep sea creatures such as tuna and whales which feed on it.

A government spokesperson told www.20304050.best the current algal bloom is being sustained by “nitrogen, phosphorous and carbon nutrients” most likely created through “ocean upwelling, river and storm water runoff, dust, dying seagrass, fish and flows from rivers and storm water”.

Waters deeper than 100m also contain high levels of nitrogen, while the deep zone of high nutrient levels is also due to the presence of bacteria that decompose sinking particles of dead organic matter.

Karenia mikimotoi feed on the same microscopic phytoplankton as well as being able to survive via photosynthesis, which is why it is proving resistant.

South Australian government response

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 karenia mikimotoi bloom.

The 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.

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.

The state Liberal Opposition want a royal commission into the algae bloom, but the SA government stopped it dead in its tracks.

Attorney-General Kyam Maher poured scorn on the proposal, suggesting it was a waste of money to investigate what was “almost universally accepted by scientists to be caused by climate change”.

“We’ve already announced half a million dollars in fee relief for the fishing industry and we’ve said we’re looking at doing more,” he said.

The state government announced a $500,000 initial relief package for fishers affected by the algal bloom, waiving certain licence and audit fees.

A government spokesperson said there will be no ban on recreational and commercial fishers

“At present there are no plans to close fishing areas as a direct result of the harmful algal bloom,” the spokesperson told www.20304050.best

Acting Premier and Environment Minister Susan Close has repeatedly said she was deeply concerned for sensitive areas such as the Coorong, and there are “things than can be done”.

“We’re looking at ways in which we can manage water in order to push the Coorong’s salinity out of the comfort zone for karenia mikimotoi,” she said.

Close said the state government recognises the widespread effects of the algal bloom on the environment, coastline, businesses and industries, adding the government has established a reference group to work with those people who are on the frontline of the algae bloom.

“The algal bloom is a dynamic situation and its effects are unpredictable but, by bringing together industry representatives and science specialists, we can continue looking at research and investment options,” she said.