Sewage not the only possible cause of norovirus says council

An outbreak of norovirus that caused the closure of nine Bay of Islands oyster farms cannot be blamed conclusively on a council-run sewage treatment plant, the High Court at Auckland has heard.

The oyster farmers are seeking $12 million from the Far North District Council as compensation for loss of earnings, general damages and remediation costs after their farms were closed in 2001 when traces of the norovirus carried in human effluent were found.

The farmers - who have not been able to reopen their farms - have identified several sources of pollution in the Waikare Inlet, but largely blamed the council-operated sewage plant at Kawakawa.

The defence opened its case yesterday with lawyer David Heaney, representing the council, saying the farmers have not proven conclusively that the norovirus originated from the Kawakawa treatment plant.

There were many other potential sources, he said. Highest on his list were the area's septic tank and onsite disposal systems. Mr Heaney said another possible source was boaties discharging their tanks into the water.

There had been some suggestion the virus strain found on the farms was not one commonly found in New Zealand, indicating it might have originated from a boat. Opua was known to be a customs clearance port, he said.

The Kawakawa plant's discharge outlet was over 15km away from the affected farms. "That is an awful long way for these viruses to survive in the open," Mr Heaney said.

A farm in Tiger Bay, which is closer to the treatment plant than the affected farms, was also not affected by an outbreak, he said.

Later that day, the court heard from William Down, the council's assets management coordinator. He read from his brief of evidence that monitoring by the Northland Regional Council had found water quality at the plant's discharge area was better than water quality upstream. Mr Down said it was never an issue nor a requirement to test for norovirus.