A rāhui has been put in place on Foveaux Strait after the parasite Bonamia ostreae was detected in the area last week.
Routine testing by Biosecurity New Zealand found the parasite on three wild oysters, sparking concerns for the local oyster industry.
Bonamia ostreae was first found in New Zealand in 2015 in oysters from the Marlborough Sounds, and then in 2017 in oysters in Big Glory Bay in Stewart Island, which led to millions of flat oysters being destroyed.
Biosecurity New Zealand spokesperson Dr Catherine Duthie said the infected oysters were not found in areas where fishing vessels had been working in the current seasons, and Bluff oysters remained safe to eat.
Dr Duthie said as of 2pm on Tuesday, a rāhui and a controlled area notice would be enacted to help protect the Foveaux Strait oyster fishery from potential spread of the parasite.
The measures, which create a 'no-take' zone around where the infected oysters were found, will be in place for an indefinite period.
"We have partnered with Ngāi Tahu, the oyster fishing industry and local authorities to determine whether Bonamia ostreae is elsewhere in the Strait and jointly agree the most appropriate measures to manage the situation," Dr Duthie said.
"While we carry out urgent sampling and testing of oysters from a range of Foveaux Strait locations, we have jointly agreed that it is appropriate to stop people taking oysters from the affected area."
The rāhui and the controlled area notice set out a 30.9-kilometre area located east of Saddle Point on Stewart Island, where it is forbidden to fish or dredge for oysters.
"These controls will not affect the availability of Bluff oysters," Dr Duthie said.
"The controlled area is small and hasn't been fished in the past five years. There are plenty of oysters available from other areas to provide a plentiful supply."
Dr Duthie said Biosecurity NZ "can't stress enough that Bonamia ostreae does not affect food safety, and fresh Bluff oysters are safe to eat."