Oyster farms in the Hawkesbury, north of Sydney, are under quarantine after an outbreak of a disease that is killing large numbers of shellfish.
Pacific Oyster Mortality Syndrome has infected or killed 90% of the oysters in Mullet Creek, where the outbreak is centred. Little is known about the disease.
"The first thing you notice is the smell because the oysters are dying, and the next one is when you pick up a basket of oysters they rattle, which is a sign that they're not healthy and not well," said oyster farmer Steve Jones.
"Then, when you pick up basket after basket it is pretty obvious that you've got a significant problem."
The ABC reports it is the second outbreak of a disease in Hawkesbury since 2004, when the QX virus swept through the area.
QX affects Sydney rock oysters, and growers switched to Pacific oysters.
"This will be the second time that their business is again wiped to zero,'' said Mr Jones.
The ABC reports the NSW Department of Primary Industries has placed 245 hectares under quarantine since Monday.