With its striking sandstone cliffs, blanket of forest and lazy backwaters, the Hawkesbury River is one of Sydney's great green lungs. Lying 60km to the north of the city centre, fringed by national parks, it is popular among sailors, fishermen and hikers.
It is also home to a creature prized by gourmands the world over: the Sydney rock oyster. The bivalve is grown on wooden racks all along the Hawkesbury and shipped to restaurants as far afield as Hong Kong, London and New York.
Or at least it was until this year. The oysters have been hit by a deadly parasite which has all but wiped them out. About 20 oyster farms on the Hawkesbury are facing ruin, and millions of oysters are dead or dying in the water.
Oyster fishermen whose families have worked the river for generations fear their livelihoods are at an end. The Oyster Farmers' Association of New South Wales says that the A$32 million ($194 million) a year industry is 'finished'. The parasite which is attacking the Sydney rock oyster is known simply as QX - Q for Queensland, where it was first detected, and X for unknown, in the days before scientists identified it.
Experts have no idea what has triggered it, although they suspect it may be something to do with the ongoing drought and the fact that rivers are not being adequately flushed out with rainfall.
The micro organism is thought to enter the oyster through its gills and then multiply in its stomach, starving the tiny creature to death. When the parasite got into the Georges River, south of Sydney, 10 years ago, it destroyed the entire oyster fishery. The same thing is happening in the Hawkesbury, where it was detected last June.
