Hundreds of thousands of dead fish were seen floating in the Darling river near the town of Menindee, around 1,000km west of the state capital Sydney.

It follows fish deaths in the same area in 2018 and 2019 where up to a million fish died from poor water flow, poor water quality, and sudden temperature changes.

The NSW department of planning and environment's water division said on twitter that "dissolved oxygen levels remain a concern for fish health" in the area.

The Australian broadcasting corporation reported today that hundreds of thousands of dead fish had been found in the river, and state fisheries officers had been sent to the area to assess the issue.