The NSW government installed four aerators in the Lower Darling region to help prevent further fish kills after the second mass death event this summer.

But Menindee local Graeme McCrabb claims they aren't working as well as they should.

"They're solar powered and have been placed under trees where they can't get enough charge throughout the day to work in the evening when they're needed," he told AAP.

Mr McCrabb, who moved to the area a few years ago because of his love of fishing and the Darling River, checks the dissolved oxygen levels in the river almost daily.

Dissolved oxygen is a key indicator of water quality and is essential for the survival of fish and other aquatic animals.

Levels between four and seven milligrams per litre mean the water quality is good but, in some parts of the river, the levels are falling below two mg/L.

"Every day I check where there could be another kill," Mr McCrabb said.

"The fish are just super stressed. Thirty-odd cod died lately and there's fish dying 150 kilometres down the river. They all start to add up."

By the third mass death there weren't many fish left to die, he said, and now the river is dominated by carp.

"Recovery for this section of the river will take a lot longer because carp are now at the top of the food chain and they eat everything."

Poor quality water further upstream where the fish deaths occurred is also trickling down to lower pools of the river and is decreasing water quality there.

NSW Regional Water Minister Niall Blair says he's happy to consider different types of aerators to help stressed fish.

Primary industries department researchers recently recorded vision of thousands of fish swimming around aerators.

"Following the devastating fish kill events over the past two months, it's encouraging to see thousands of fish swimming in the vicinity of the aerators," Mr Blair said in a statement on Friday.

"We've always said aerators are not a silver bullet but they are working well as a localised measure to save some key fish species."

The DPI has also relocated some 100 fish from Menindee to healthier waters hundreds of kilometres downstream at Narrandera.

Mr Blair said they're adjusting well to the new surroundings.

"We know that moving 100 fish doesn't compare to the hundreds of thousands that were lost but I am hopeful that these small relocation projects will allow us to breed hundreds of thousands of fingerlings that can find a home once again in the much loved Darling River," Mr Blair said.

Australian Associated Press