More fish are likely to die in NSW as state and federal water managers prepare for an emergency meeting to canvass options to mitigate the ecological disaster.
Water Minister David Littleproud described the situation as horrible, joining his state counterpart Niall Blair in warning of more devastation after up to a million fish died in the Darling River system.
"I'm advised there is a high likelihood of more fish kills very soon," Mr Littleproud said in a statement on Monday.
The federal government wants states to agree to use $5 million from Murray-Darling Basin funds for a strategy to look after native fish.
Mr Littleproud has asked the Murray-Darling Basin Authority to convene a meeting of state and federal water managers and environmental water holders this week.
The meeting will look at the immediate risk of further fish kills and how to mitigate that possibility including through the release of environmental water.
Stakeholders will also review state and federal watering priorities to see if changes are needed.
Prime Minister Scott Morrison said he was concerned some may attempt to "play politics" with the bipartisan Murray-Darling Basin Plan.
"It's a devastating ecological event," Mr Morrison told ABC News Breakfast.
"For those who live all throughout the region, just the sheer visual image of this is terribly upsetting."
Labor wants an emergency task force to investigate how and why the fish died, including the potential impact of agricultural chemicals like fertiliser.
Opposition Leader Bill Shorten also wants it to look at whether water diversions or management in the Murray-Darling system made the disaster worse.
Scientists argue mismanagement of the river system is to blame, but the NSW government insists the devastating drought gripping the state is a key factor.
"Drought is a natural event. Blue green algae outbreaks and fish kills of this scale are not natural events," Mr Shorten wrote in a letter to the prime minister.
Mr Littleproud and Mr Morrison pointed to barren conditions as the central factor behind the fish deaths.
"The reality is we're in a serious drought and the only silver bullet is rain," Mr Littleproud said.