Traces of the virus which causes COVID-19 have been detected in a sewage treatment plant at Ulladulla for the first time.
Although there are no new cases of the illness itself on the South Coast, residents have been told to monitor their health closely. If symptoms do appear, the person should get tested immediately and isolate from other people.
NSW Health said the treatment plant served a population of 32,000 people, taking sewage from Narrawallee, Milton, Mollymook Beach, Ulladulla, Kings Point, Burrill Lake, Dolphin Point and Lake Tabourie.
"This could mean there are undetected cases of COVID in the community or someone with the virus visited the area," the health department said, "so we are asking everyone in that area to be especially vigilant in monitoring for symptoms, and if they appear get tested and isolate immediately."
The development came as New South Wales gave its daily update on the virus.
"NSW recorded four new locally acquired cases of COVID-19 in the 24 hours to 8pm last night," a statement said.
"Seven cases were also recorded in returned travellers, bringing the total number of COVID-19 cases in NSW since the beginning of the pandemic to 4,806."
Of those four new local cases, one was still being investigated and the other three were close to people who had already caught the virus.
One of these cases, a man from the northern zone of the Sydney's northern beaches first reported yesterday but included in today's numbers, remains under investigation.
Another is linked to the Croydon cluster. There are now 11 cases in this cluster.
And two cases are linked to the Berala cluster which brings the total number of cases in this cluster to 20.
Seven cases were also recorded in returned travellers, bringing the total number of cases in NSW since the beginning of the pandemic to 4806.
There were 26,112 tests reported to 8pm last night, compared with the previous day's total of 27,879.
NSW Health continues to urge everyone throughout the state to continue to come forward with even the mildest of symptoms
Across the border, Greater Brisbane will enter a hard lockdown from 6pm on Friday after a cleaner at a quarantine hotel was diagnosed with the highly contagious UK strain of COVID-19.
Residents in the council areas of Brisbane, Logan, Ipswich, Moreton Bay and Redlands will be required to stay at home until 6pm on Monday except for essential work, exercise, essential shopping and to access healthcare or to look after the vulnerable.
The Service NSW app, which hosts a mandatory check-in system for hospitality venues, stopped working for several hours on Thursday afternoon.
It has been compulsory to use the app in some businesses since the start of 2021.
Separately, the police said they were contacted after a man allegedly assaulted and spat on a security guard at a shopping centre at Nowra about 11am. Police were told the man threatened the guard and told him he had COVID. The man was arrested and charged with common assault and not complying with COVIS-19 regulations.
Meanwhile, the second day of the Australia-India Test will be played at the SCG on Friday, with all attendees forced to wear masks except when eating or drinking.
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