Clean-up 'urgent' as fish rot in NSW river

The dead fish need to be collected "within a matter of days", before they sink to the bottom of the river and become almost impossible to retrieve, according to environmental scientist Stuart Khan.

If they remain in the water, bacteria that feast on the carcasses will proliferate and rob the water of oxygen, the environmental and civil engineering professor told AAP.

Meanwhile, the decaying fish will release chemicals that could trigger an algal bloom, which sparked this mass death event earlier in the week.

"Dead fish are great fertilisers, they release nitrogen and phosphorus and that's what causes algal growth," said the University of New South Wales professor.

"Therefore the whole cycle goes through again, that's why there's some urgency to remove the fish."

Local Kate McBride said the town of Menindee "stinks" and she was concerned over further deaths.

"More oxygen will be taken out of the water and the remaining fish, which are pretty much only carp, are going to continue to die - further fish kills will be seen undoubtedly," she told AAP.

Residents are pointing the finger at state and federal governments for draining too much water from the Menindee Lakes and over-allocating the precious resource to irrigators.

But the peak body for irrigators - the National Irrigators' Council - has hit back, insisting farmers at the north of the river have received no water allocations in the past 12 months.

Scientists argue mismanagement of the river system is to blame although the NSW government insists the ongoing drought is a key factor.

Australian National University honorary professor John Williams says the current Murray-Darling Basin Plan has "failed" and needs to be overhauled.

Australian Associated Press