Predictions that the La Niña weather pattern will continue until the end of January have alarmed farmers.
A wet summer will make it impossible to harvest many crops, and what does make it to the silo is likely to poor quality.
Euabalong farmer Damien Doyle has told his workers to evacuate ahead of a big flood coming down the Lachlan River in Central NSW.
Floodwater has inundated his paddocks and 1,000 hectares of wheat and barley is under water.
"You can't even see the crop anymore," Mr Doyle said.
"There's a lot of damage from waterlogging, and just getting onto the paddock is the big challenge."
The latest long-term forecast from the Bureau of Meteorology has predicted a wetter than average summer with a strong chance of severe storms.
Planting summer crops will be too difficult for many farmers across the state if the wet conditions persist and that means farm incomes will be significantly down.
NSW Agriculture Minister Dugald Saunders said the damage bill would probably run into hundreds of millions of dollars and a lot of crops would be lost.
DPI climatologist Anthony Clark said he thought that estimate was about right.
"In that order of magnitude, yes, but it is always difficult to put a figure on it this early," he said.
Rabobank analyst Denis Vosnesenski said a quarter of the crop that was expected to go in had not been planted due to flooding and what was harvested would have quality issues.
"We will be revising down our harvest figures for NSW crop," he said.
More disaster assistance announced
Mr Saunders has announced an extension of a disaster declaration affecting 27 local government areas, which triggers financial support for landholders.
He urged producers to report flood damage to their properties, including land, infrastructure and animals, as help is available.
“We are assisting farmers in western NSW with emergency fodder drops because their livestock was stranded,” he said.
The federal government announced it would pay people in those areas who have lost income a disaster recovery allowance equivalent to a 13-week payment at the JobSeeker level.
Long, wet summer
The flooding is expected to last for several weeks in many parts of NSW.
The Department of Primary Industries climatologist Anthony Clark said a wet summer lasting until January was the last thing farmers needed.
"The tragedy is that many farmers earlier in the year had crops that showed a lot of promise, a good yield," he said.
