Batemans Bay Oysters director Jim Yiannaros said the Clyde River was closed to harvest on February 25 because rainfall had reduced the water salinity below state regulation levels. He said it was not unsafe, but a "precaution" to ensure oyster quality.

It has hardly stopped raining since then, and the river has not reopened for harvest.

Oyster farmers have not been able to harvest their product in that time, causing a shortfall in supply.

Oysters act as filters, feeding on all the plankton and algae in the water. They also filter any contaminants in the water, which can build up in the gut of the oyster and reduce the quality of the product. Therefore, oysters can only be grown and harvested in the cleanest of waterways and the NSW Department of Primary Industries has strict regulations surrounding oyster harvesting.

The Clyde River has already been closed for two weeks, and Mr Yiannaros said last weeks torrential rain only delayed the re-opening of the river to harvesting.

The best case scenario, according to Mr Yiannaros, was water testing resuming in a fortnight. Only then could oysters be harvested again. That timeline, he said, depended on no rain in the next two weeks.

"Because everything is so wet, any rainfall runs straight into the river," he said.

"If we do get more rain, it will set us back again."

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The Clyde River catchment extends to just west of Ulladulla, and therefore the heavy rainfall experienced north of the Eurobodalla will travel through the system too.

While this strict water quality regulation creates a supply shortfall, it ensures the quality of oysters produced in the region.

"Once oysters are back in supermarkets and restaurants, you know the quality is good," Mr Yiannaros said. "The quality - the safety - will be there."

"We just have to be patient and wait for mother nature to clear the water and for us to test it.

"She normally does a good job."

Mr Yiannaros said pacific oysters were not as hardy as Sydney rock oysters, and there had been some fatalities caused by all the fresh water into the estuary system.