"It was Armageddon," McCrabb tells the Herald as he steered his boat to remaining clusters of carcasses on Wednesday. "You can't get [the scale] until you've actually seen it. It was river bank to river bank of dead fish."

Again, the trigger was a weather change that brought relief at least to the human population. After touching a blistering 46.2 degrees on the preceding Friday, temperatures plunged to lows of 19 and 16 on the Saturday and Sunday morning.

For the carpet of blue-green algae that had set in over much of the pool beyond Weir 32 on the Darling, that cool snap was traumatic. The dying algae released toxins, as well as further depleting dissolved oxygen levels in the water, choking those fish that could find no refuge.

Video footage of that first day's carnage shot by Gregory quickly circulated rapidly on social and mainstream media. Imagery posted by local grazier and Menindee campaigner Rob McBride holding up a dead Murray cod further stoked public interest, reaching almost 6 million people by Thursday.

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'Turning off life support'

For Iain Ellis, a fisheries manager with NSW's Department of Primary Industries who visited the devastation on Monday, the kill was not a huge surprise.

The region had been under a "red alert" for algal blooms for weeks. A large culling was almost inevitable given the lack of fresh flows coming into this - and much of the entire course - of the Darling.

"The net result [of the dissolved oxygen depletion] is you can kill everything, particularly your less robust fish, like the bony herring [also known as bony bream]," Ellis says.

Usually inured to nature's extremes, native fish species tolerance levels had been taking hit after hit. The challenges include drought and heatwaves, high nutrient levels from farm run-off, regulation of flows, and introduced fish like the carp.

"They are animals pretty much on life support, and you turn off their machines," Ellis says.

And that's before climate change is added to the brew. The Murray-Darling Basin is on a long-term drying trend made worse by rising temperatures. Last year was one of the basin's driest in the past 109 years, while it was the region's hottest by maximum temperatures, bureau data shows.

$13 billion plan

But it is not as though taxpayers haven't been forking out to restore the health of Australia's most important river system. This week's fish kill suggests the Murray-Darling Basin Plan isn't working.

"We've spent $13 billion dollars on the plan, a million fish die here - there's a missing piece," McCrabb says as he steers the tinnie back towards a makeshift canopy favoured by locals out for a fish in better times. "There's not anyone on the Darling who would say it's in a better shape than before it started [in 2012]."

National attention

Maree McCrabb says there's every reason the Darling should be in the national spotlight given the importance of the river itself and the crucial role it plays in breeding fish such as the Murray cod or the endangered silver perch.

"It's like trying to fix the Great Barrier Reef," she says as she prepared for a 16-hour drive back to Brisbane where she and her husband run a pool maintenance business, dividing their time between Queensland and Menindee.

Being remote for most city dwellers, the Darling's health "doesn't get attention", Maree says.

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With state elections due in late March and a federal election in May, that could change.

The Menindee fish calamity - followed this week by two smaller ones on the Namoi and Lake Cathie - could make the state of the rivers a fierce political battleground.

Michael Daley, NSW Labor's leader, fired an early foray, demanding on Thursday a special commission of inquiry into the "ecological catastrophe" at Menindee and beyond.

Niall Blair, the NSW Fisheries Minister, interrupted his holiday to make a flying visit to Menindee on Wednesday. His plan to land at the local boat ramp - still littered with stinking, decaying fish - was aborted after 150-odd protesters gathered to greet him after threats of harm were made on a Facebook post.

Blair is adamant drought was the main trigger for average flows into Menindee diving to 30 gigalitres in the past half year from an annual average of 4000gl.

His department will conduct an urgent study into the fish deaths and the subsequent clean-up but there would be no budging from plans to spend some $150 million on a reconfiguring of the lakes to reduce evaporation and avoid the need to find environmental water savings of 105gl a year.

NSW Labor is sticking by plans to scrap the project - even though it has Federal Labor support and from the Labor states of Victoria and Queensland.

"They don't understand what it would mean," Blair says, of the NSW Labor stance. "You would blow up the [Murray-Darling] plan."

McCrabb, who met Blair during his Menindee visit in his role on the town's tourism committee, says locals - whether Indigenous or not - will need a lot of convincing the engineering projects planned for the lakes make sense. The 105gl is planned savings a year "is just a fictional number", he says. "It doesn't exist - why not make it 210?"

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“Why empty the lakes when there’s no need,” echoes Badger Bates, a Barkandji elder. “Where’s our share of the water.”

Bates, who worked as a national parks ranger for more than 20 years, says the Menindee Lakes was home to many important sites for the traditional owners dating back tens of thousands of years, making the region worth sharing the protection of near Mungo Lake.

"Now they want to come back and muck around with the lakes more," Bates says.

Making its own weather

McBride - whose 230,000 hectare Tolarno station is the largest "husband and wife" farm in NSW - says it's also wrong to assume evaporation from the shallow lakes means the water is "lost to the environment".

"When Menindee Lakes are full, we'd get one or two more inches of rain," he says.

"It creates its own storm," he adds. "We're affecting our weather patterns."

In the town, residents complain of the odour of the water they have to use, sucked from the river in large pipes.

"Even washing your clothes, it's enough to make you sick," Mavis, the manager of the local provisions store, says.

Science feast

About the only beneficiaries from this week's die-off have been the fish scientists.

While not cheering, fisheries experts have leapt at the chance to learn more about the fish "without sacrificing them", as one told the Herald after a day on the river.

Murray cod caught by anglers have to be thrown back if they are 55-75 centimetres in length, McCrabb says. Specimens he collected - including from the December kill event - and kept in cold storage for scientists to gather included one more than 1.25 metres long, likely many decades old. The scientists don't actually require much of the fish to study - which is just as well as even by mid-week the bulk of the carcasses had started to decompose and sunk to the river floor if they hadn't been picked off by waterbirds first. "We don't get a lot of information about the big fish," Fisheries manager Ellis says.

Otoliths, tiny ear bones that help the fish balance in the water, are almost all they need. The extraction process, quick as it is in skilled hands, still requires dissection of often pungent fish.

"It's hard - you get used to it in this field even [this week's] been kind of extreme," Ellis says. "My wife's not too happy when I get home...which is why I have to wash down out on the lawn."

Those ear bones are being spirited away to a new Department of Primary Industries laboratory at Narrandera, almost 600kms from Menindee, where lasers will be used to make remarkable findings about the age of the fish and where they spawned and lived.

Replicating nature

The presence of rare earths such as strontium and barium, which vary along the Murray and Darling rivers, will help reveal how best to use scarce water reserves. "We try to replicate [nature] with environmental flows if we know more," Ellis says. "We can try to induce [the fish] to spawn."

While the political and media hype over the river's health may be dissipating almost as fast as the fish, it's not clear Menindee or other parts of the basin have seen the last of such events.

By Friday, the region was bracing for another heatwave of low-to mid-40 degree weather - as is much of the inland region - with some concern about possible fish kills on the Murrumbidgee.

"It's going to be a long summer," Ellis says.