A critically endangered water bird could have a harder time this breeding season after the federal government paused environmental water releases in NSW.

The Macquarie River is one of the regulated systems impacted by the unexpected delay with the Macquarie Marshes an area of serious concern for scientists and other stakeholders.

Wildlife ecologist Matt Herring said the Australian Painted Snipe breeds best in a combination of shallow water, mud flats and water plant cover provided by the wetlands.

However, the health of the Macquarie Marshes relies heavily on environmental releases, and Mr Herring said the pause announced by the Commonwealth Environmental Water Holder (CEWH) on 18 August could have a "significant" impact on the population.

"It is urgent because birds like this are coming into the start of their breeding season and they're looking for the very best sites that the landscape has to offer," Mr Herring said.

"It's an area that they're familiar with from last season and without any environmental water available they won't be catered for.

"This situation is just as relevant to a whole bunch of other biodiversity, not just birds."

'Thomasina' was caught and tagged on Saturday 5 October. [PHOTO: Australian Painted Snipe Information and Tracking Project]

Under a recent new interpretation of water rules, Water Holder Dr Simon Banks said water reserved under an environmental license needs to be metered.

He said the change has prompted him to "temporarily" stop water being released into river systems until he is confident that CEWH is compliant with regulations.

In the early 2020s, government authorities put Australian Painted Snipe population at around 340 mature-aged birds after declines over the previous five years.

Last year, researchers including Mr Herring made a rare set of Painted Snipe catches in the Marshes, allowing them to tag and track the birds.

"Finding a legal solution to this water metering issue as urgently as possible would mean that species like the Painted Snipe are not impacted as much as they could be," Mr Herring said.