The Associate Minister of Health is not aware of any recovered cases from the delta outbreak having travelled to Bay of Plenty.
Covid-19 was detected in a wastewater sample collected last Thursday in Tauranga.
Dr Ayesha Verrall told Morning Report it could be a new incursion, or it could be something else and anyone in Bay of Plenty with symptoms should get a test.
"There have been instances of false positives in wastewater, so we just need to take a cautious approach for people who have symptoms should get tested."
Further samples have been taken and results are expected tomorrow.
It could be a recovered case still shedding the virus, or an undetected acute case.