The downgrading of grain crops in New South Wales may not be as severe as first thought.

It has been a rollercoaster season for croppers who have been hammered by some extreme weather events, including major flooding, hail and above average rainfall.

Water damage has affected up to 700,000 hectares of crop.

Grain experts at the NSW Department of Primary Industries said districts that avoided serious waterlogging had a better chance of producing decent yields.

Peter Matthews, technical specialist for grain services said there was potential for that in the state's southern grain belt.

"If you haven't been on a major river, a lot of crops that haven't seen waterlogging have been doing extremely well and they're going to see above average yield," he said.

"Probably in the four to five tonne range, when normally they'd be sitting back around the three to four [tonnes].

However, he said grain quality would be a question mark, depending on whether protein levels were maintained because of such high yields.

"We may see a lot of grain coming into the system that is of lower protein and may not make AH [Australian Hard] or Prime Hard that we would normally see in that zone."

Windrowing canola in NSW will start cranking up in the next few weeks to preserve yield.

The DPI's oilseeds technical specialist Don McCaffery said most crops would be hit by some form of water damage.

"In NSW we think we've been underestimating the area sown right through the season.

"I'd be fairly confident in saying we've lost at least 10 per cent of the crop through waterlogging damage and flooding damage.

"So that's going to amount to 50,000 to 60,000 hectares as a minimum."

At current canola prices, those losses are worth around $50 million," he said