According to NSW Health, wastewater from Bathurst returned a positive sample, which could indicate "a current or a previous infection in someone who attended or worked at the Bathurst 1000".
Anybody who attended the event is therefore being urged to get tested should they have any symptoms.
"NSW Health is tonight calling on anyone who attended the Bathurst 1000 motor race on the weekend, as well as residents of Bathurst with any symptoms that could signal COVID-19, to get tested as soon as possible after remnants of the COVID-19 virus were detected in raw sewage in the area today," read a statement.
"The sample comprises wastewater from over the past weekend, and could indicate current or a previous infection in someone who attended or worked at the Bathurst 1000 motor race, a visitor to Bathurst, or even a local resident.
"Visitors to and residents of Bathurst must be aware of any symptoms of illness, and immediately isolate and get tested should even the mildest of symptoms appear that you think might just be a cold.
"Symptoms like a runny nose or scratchy throat, cough, tiredness, fever or other symptoms could be COVID-19.
"After testing, you must remain in isolation until a negative result is received.
"NSW Health is urgently undertaking investigations, which include reviewing lists of all those known to have had the virus who attended or worked at the race."
The alert is valid not just for the 4000 spectators allowed through the gates each day, but also the drivers and crew from Supercars and the four support categories.
Most Victorian based personnel have returned home this week, after more than 100 days on the road, while the majority of those from the paddock Queensland-bound are serving a quarantine of sorts in Kingscliff in northern New South Wales before being allowed across the border.