COVID-19 has been found at the Victoria Point and Luggage Point wastewater treatment plants.
The Victoria Point plant handles waste from Redland Bay, Thornlands and Victoria Point.
Traces have previously been found at Cleveland.
Queensland Chief Health Officer Jeannette Young said anyone with COVID-19 symptoms, no matter how mild, should get tested.
"Symptoms include fever, cough, sore throat, runny nose, fatigue, diarrhoea, nausea or vomiting, and loss of taste or smell," Dr Young said.
"It is very important people with symptoms come forward right away and get tested - now more than ever - with the new cases we are seeing in other states and the amount of interstate travel that we've seen over the past while.
"It is critical we detect any cases that we may not be aware of as quickly as possible through our testing system, to contain any potential spread.
"We are concerned by the new variants that are emerging overseas that are more contagious than previous variants we have seen in Queensland.
"It's also possible that this detection relates to previous COVID-19 cases that can shed viral fragments for a couple of months after they are no longer infectious."
For more information about Queensland's wastewater surveillance program, visit the Queensland Health website.
To access a full list of COVID-19 testing locations, with interactive map and post code search, visit qld.gov.au/covid19testing.
If your local testing clinic is crowded, others are available.