High levels of toxins capable of causing paralytic shellfish poisoning have had little effect on shellfish farmers in the Queen Charlotte Sound.
Marine farming association executive officer Graeme Coates said being wary of various toxins, and paralytic shellfish (PSP) poisoning, was "part of the business".
There were PSP events occurring regularly and marine farmers did not harvest shellfish when it was present, Mr Coates said.
However, a presence of the toxins meant harvesting shellfish could not go ahead until the levels had dropped, he said.
The mussel industry was not overly effected because there were not many mussel farms inside the Queen Charlotte Sound.
Independent mussel farmer Dave Norton said although the toxin was inconvenient, it was more important that his mussels were safe for consumption.
"I don't want it there because I want to harvest my mussels, but it's a toxin that can hurt people," he said.
Tio Point Oysters co-owner Bruce Hearn said his Oyster Bay farm had not yet been affected, but it was being closely monitored.
"The reading from yesterday is [the toxins are] below detectable levels at Oyster Bay," he said.
"As soon as it gets close to the regulatory limit, we'll close but our products are still very safe."
The public should still be wary of consuming shellfish from the Queen Charlotte Sound, because Oyster Bay toxin levels were not necessarily indicative of the entire area, Mr Hearn said.
Lack of a southerly wind meant the toxins had been moving away from Oyster Bay, but if that changed the toxins may be pushed into the area.
They would be testing their toxin levels twice a week, as opposed to once a week, he said.
"We are watching very very closely . . . public safety is the primary consideration," he said.
Nelson Marlborough District Health Board medical officer Dr Jill Sherwood issued a warning to the public not take or eat shellfish from Queen Charlotte Sound on Tuesday.
Kina, mussels, pipi, tuatua, oysters and cockles harvested from the affected areas since February 19 were unsafe to eat because of the high level of PSP-causing toxins, she said.
The affected area covered all of Queen Charlotte Sound, including Tory Channel.
A shellfish closure map shows the affected area is all of Queen Charlotte Sound from a line drawn between Cape Jackson, across to Cape Koamaru, including Tory Channel out to East Head and West head.
Symptoms of poisoning were numbness and tingling around the mouth, face or extremities; difficulty swallowing or breathing, dizziness and double vision. In severe cases, paralysis and respiratory failure can occur.
Acute symptoms usually occur within 12 hours of consuming shellfish.
For more information about the safety of shellfish contact the on-call health protection officer Blenheim on (03) 520 9999.
- The Marlborough Express