She said while fragments in waste water could be present for a number of reasons - it pays to be cautious.

"I'd urge anyone in the Portland area with even the slightest symptoms to get tested and to isolate until they receive those results," Ms Britnell said.

"The state government must offer full support to those cross border community members who are fatigued from months of border restrictions and the burdens they have caused.

"They were beginning to see light at the end of that very long tunnel, but are now being asked to go through that all over again."

UPDATE 2PM: Glenelg Shire Council mayor Anita Rank has urged the Portland community to get tested for coronavirus after the Department of Health and Human Services advised fragments of the virus were detected in untreated wastewater taken from the Portland wastewater treatment plant on Tuesday, November 17.

"Whilst the source is still unknown, I urge community members to please get tested if you are showing any flu-like symptoms, no matter how mild," Cr Rank said.

"What we are seeing in South Australia is a timely reminder to our community that the virus can present itself and spread very quickly. We need to remain vigilant.

"We ask the community to continue to adhere to the health advice and practice social distancing, wear your face mask correctly always outside of your home and ensuring you wash your hands regularly and thoroughly. Following these simple measures can help to reduce any potential spread within our community."

Coronavirus testing is available through Portland District Health and an alternate testing site will be established at Alexandra Park to accommodate for overflow if required.

Earlier 11.30am: Portland's chief health officer has requested people with the mildest symptoms get tested for coronavirus after a positive sewage sample.

Portland District Health chief executive officer Christine Giles said COVID-19 fragments were found in the city's sewage in a sample tested on Tuesday.

Those results will be made public today.

"There were positive COVID fragments found," Ms Giles said.

"It could be from an old case, someone shedding, but there is also the possibility that there is an active case in the community.

"We are requesting that anyone with the mildest of symptoms come into the drive-thru facility at the Portland hospital and get tested."

Ms Giles said the positive fragment test result was a reminder that people needed to do the right thing.

"There's certainly no cause for panic, but the last thing we want is for the genie to get out of the bottle," she said.

Ms Giles said hundreds of people leaving South Australia before the six-day lockdown was imposed was another reason for caution.

Three plane loads of people left Adelaide and landed in Sydney on Wednesday, while the South Australian/Victorian border remained open to vehicles.

"I don't know what's coming across the border, I have no extra intelligence on that," Ms Giles said.

"I suppose it's human nature for some people to try and avoid the South Australian lockdown.

"I certainly don't expect people in Portland to react negatively to South Australians like we saw when Victorians went to South Australia for essential work during the second wave."

The health service CEO said she had two messages for the community.

"We need to be kind to each other, whether that's local or anyone from interstate," she said.

"Portland District Health is well prepared and testing is available to anyone with the mildest symptoms or anyone from a South Australia hot spot.

"Those 40 plus hotspots have been identified on the SA Health website.

"We are more than happy for anyone who has been to one of those hotspots to come through and get tested at the Portland drive-thru site.

"We would ask people to self-isolate until they get those test results back."

Ms Giles said everyone wanted to keep their community safe and getting tested was the best way for that to happen.

"Testing is critical. It enables us to find and pin down the outbreaks. The onus is on people to do the right thing and that's what's happened in the past," she said.

"If people are self-isolating in holiday accommodation, after getting tested, please give us a call and we can provide supplies until your tests are back.

"Support is also available through the 1800 Glenelg Together helpline on 1800 512 461," she said.

Portland has had two coronavirus outbreaks during the coronavirus pandemic, both being quickly brought under control.

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