Three of the days could top 44 degrees, or nearly 10 degrees above the January norm.
"Droughts would have contributed to the blue green algae outbreak", he said.
"They are rotting, they're large corpses, they're bloated in the water".
In the town itself, the stench from rotting fish carcasses near the main boat ramp wafts into the Burke and Wills Menindee Motel.
Niall Blair, NSW's fisheries and regional water minister, blamed the deaths on drought. "I visited yesterday to see what decades of mismanagement and corruption have resulted in - an ecological catastrophe".
Cotton Australia said drought was affecting the river system and that the industry was also suffering, forecasting its crop this season would be half of the previous year's.More news: Elon Musk teases what SpaceX’s Starship test vehicle will look like
"The [Coalition parties] have been repeatedly warned by far west residents, community groups, scientists and Labor that their water policies would cause devastation on the Darling River".
"You can not dismiss the fact there is a drought and a lack of water".
A lack of water in the Darlin River and the Menindee Lakes means that authorities were unable to flush the system before millions of fish suffocated through a lack of oxygen in water.
Taxpayers have stumped up more than $13 billion to restore the health of the basin. "Without more water available to flow through the system, it is possible more fish will die during summer".
The immediate cause of Menindee's calamity was a change in temperatures that killed much of the blue-green algal bloom on that part of the river.
"The scale of this disaster is extraordinary and unprecedented", the opposition leader said in a statement.More news: Leeds United employee 'seen acting suspiciously' outside Derby County's training ground
NSW Labor confirmed that it would seek to overturn the plan - supported by all basin state governments and the Morrison government - to effectively decommission the Menindee Lakes System.
He added that 250,000 livestock and millions of native animals are at risk from the increasingly toxic river water. He added the SDL project at Menindee, which aims to save 105 gigalitres a water a year, must proceed. Some of them were up to 100 years old, the men said. "You would blow up the [Murray-Darling Basin] Plan".
Ex-Greens MP Jeremy Buckingham has made himself an instant meme after almost spewing while holding a dead fish in a video that was meant to highlight the National Party's water policies.
"It's radio -f*#$ing active but you can go for it", someone comments off camera before Mr Buckingham plunges head first into the water.
He said the problem could be traced back to management of water by state and federal levels of government and both of the major parties.
The cotton industry says it is not to blame for the mass deaths of hundreds of thousands of fish in the Darling River and is exhausted of being a "whipping boy" for problems associated with the drought.More news: Lana Del Ray Releases New Single
A South Australian royal commission was held in 2018 to investigate allegations of widespread water theft from the Murray-Darling Basin by rogue irrigators with its report expected on February 1.