Such a move, part of the Sustainable Diversion Limits projects, would "further reduce water flows in the lower Darling River and destroy fish breeding grounds in the Darling River", Labor said, adding it had "committed to abandon this plan to prevent further ecological destruction".
"What stinks more than this dead animal is the management of this river. and the absolute decimation of the river by cotton irrigators upstream", independent NSW Member of Parliament Jeremy Buckingham said in viral video posted to social media on Thursday.
"Mature fish that survived decades of droughts could not survive the Liberal-Nationals' water policy", Mr Daley said.
"It was one of the most disgusting experiences of my life".
"I felt so sick that I panicked and jumped in the river to escape it - as bad as it is!"
"The overwhelming stench from millions of dead fish floating in the Darling River at Menindee is grotesque".
Scientists argue mismanagement of the river system is to blame although the NSW government insists the ongoing drought is a key factor.
Niall Blair, NSW's fisheries and regional water minister, blamed the deaths on drought.
"Coupled with the extensive drought and the simple fact there has been little-to-no rain, the release of water from the lakes has exacerbated the conditions leading to these fish deaths".
Days on from Sunday's discovery of the huge fish kill, fisheries staff have mostly left and the bulk of the corpses of bony herring, perches and Murray Cod are disintegrating or sinking from view.
"On the Barwon-Darling, the impact on cotton production is even more devastating with zero hectares of cotton being grown in Bourke this season, down from 4,000 hectares the year before", the general manager of Cotton Australia, Michael Murray, said.
Mr Buckingham was standing on the side of the river with local farmers Dick Arnold and Rob McBride, brandishing the rotting carcass of a native, critically endangered Murray cod to highlight the environmental emergency when the smell became all too much. This is not because of the drought, she says, it is "man made" and could have been avoided had several years of water in Menindee Lakes not been squandered.
The latest kill follows an incident in December resulting in more than 10,000 fish mortalities along a 40km stretch of the Darling River.
The fish deaths disaster in NSW could become an issue in South Australia's royal commission into the Murray Darling Basin.
The immediate cause of the mass fish kill is believed to be a sudden drop in temperature that killed algal blooms in the water, depleting it of oxygen and causing fish to die.