Carp have been filmed floating and gasping on the banks of the Darling River at Menindee after the town in far west NSW was struck by another mass fish kill.

Key points: This is the third fish kill in the far western NSW town of Menindee in less than two months

This is the third fish kill in the far western NSW town of Menindee in less than two months Rainfall and a major cool change may have worsened the algal bloom in parts of the Darling River

Rainfall and a major cool change may have worsened the algal bloom in parts of the Darling River Fisheries officers are on their way to the site to commence investigations

The NSW Government is investigating after thousands of fish were found dead Monday morning — less than a month after about a million fish were killed in the same area.

Fisheries officers from NSW's Department of Primary Industries (DPI) are on their way to the river to confirm the number of fish killed.

Large numbers of bony bream and a smaller number of other species have perished, according to the DPI.

Video shows the grim scene that greeted locals Monday morning of exhausted fish gasping on the water's surface.

Blue-green algae removes oxygen from the water when it decomposes. ( ABC News: Sarah McConell )

Water Minister Niall Blair said there had also been reports some Macquarie perch were involved, but no confirmation Murray cod had perished.

The weather conditions had been similar to early January, when the first mass fish kill occurred, Mr Blair added.

"Unfortunately, we’re expecting the conditions to potentially continue to deteriorate," he said.

Clean-up crews were due to begin work Monday afternoon, he said.

Menindee gathered worldwide attention after the last fish kill.

It followed a smaller kill at the end of 2018.

Those two kills were the result of a blue-green algae bloom which stripped the water of oxygen, suffocating the fish.

Algae blooms can worsen during severe temperature change and rain.

On Sunday, the temperature in Menindee dropped 20 degrees Celsius and 2.1 millimetres of rain fell.

The Central Darling Shire Council has deployed a clean up operator who is also tasked with reporting on the fish.

'There will be none left'

Sorry, this video has expired Labor says mass fish kill shows it's time to for scientific advice, not debate

Federal Opposition Leader Bill Shorten said the latest kill proved there was "the makings of an ecological" disaster in Australia's most important river system.

"This is a disaster, the disaster keeps on unfolding," he said.

NSW Government officials say the state's drought was to blame for the fish kill earlier this month, but locals in Menindee claim the area's waterways have been mismanaged for years.

They said these fish kills proved their worst fears about the emptying of the Menindee Lakes in 2014 and 2017.

Small bony bream are the latest victims to the algae bloom on the Darling River. ( Supplied: Graeme McCrabb )

Menindee Tourism Association president Rob Greggory said the event was "tragic".

"What we are seeing is probably the last lot of fish that are here now," he said.

"There will be none left."

Mr Greggory said it was disappointing the Prime Minister or Federal Environment Minister had not visited the area.

"It would be nice for them to see it with their own eyes, instead of looking through the lens of a camera," he said.

Locals say there is an awful stench at the site where the fish died. ( ABC News: Sarah McConell )

NSW Premier Gladys Berejiklian faced criticism for a whirlwind visit to the lower Darling on Friday that did not include Menindee.

When questioned as to why she did not stop in, she said it came down to prioritising.

"Menindee has a population of 300 and they are on level one," she said.

"Others are on level five and six.

"I have been on the ground and spoken to people and been within a few kilometres of these specific issues."

Ms Berejiklian said water security in the state's far west had been a priority for her Government.