Two prawn farms on the Logan River in South East Queensland have returned positive test results for white spot disease more than three years after it was first detected in the area.

Key points: White spot has been found in two prawn farms on the Logan River

White spot has been found in two prawn farms on the Logan River The results followed positive test found in crabs in Moreton Bay

The results followed positive test found in crabs in Moreton Bay Farms are being told to not pump water in or out of the Logan River

Last month Biosecurity Queensland undertook routine surveillance in Moreton Bay with mangrove swimming crabs returning preliminary positive results.

Subsequent samples from two prawn farms on the Logan River also returned positive results.

The results were confirmed with testing by the Australian Centre for Disease Preparedness (ACDP) in Victoria.

Queensland's chief biosecurity officer Malcolm Letts said the two farms that tested positive had completed their harvest.

"There are only four farms in production on the Logan River and one had already finished their harvest," he told ABC Radio Brisbane.

"The other two that tested positive had all but finished their harvest and the fourth farm is still harvesting and tested negative.

"The movement orders stay in place with the disease where it is, and we've been able to keep it contained in the south east corner."

It is another set back for prawn farms along the Logan River which were only six months away from officially being declared white spot free.

Farmers are being told not to pump water into waterways. ( ABC Rural: Marty McCarthy )

"There was only one more round of testing before we had the two years completed to get proof of freedom, so the industry is very disappointed."

He said farmers had been directed to not pump water out into the Logan River or bring water onto farms to ensure the risk of disease transfer was minimised.

"It's a destructive disease in relation to prawns themselves and if you get white spot on your farm it will affect the entire crop you have," Mr Letts said.

"The farms which have been operating have improved their biosecurity standards to a very high level and that's allowed them to operate for the last two harvests.

"This disease is very hard to trace in terms of if it's come from the wild into the farms or vice versa."

White spot disease does not pose any human health or food safety concerns.

Queensland Seafood Industry Association spokesperson Eric Perez doubts the discovery will change people's buying habits.

"Nothing really changes as all the restrictions are in place and people are still buying prawns in bulk," he said.

"If nothing was done to try and contain the spread then it would be a worry, but government and industry have done what they need to do.

"We will continue to do what we do best and sell prawns to Queenslanders who enjoy them."

Biosecurity Queensland representatives will meet with members of the Aquatic Consultative Committee on Emergency Animal Disease this week to discuss ongoing management options.