A health warning advising people not to swim in a section of the Ngongotaha Stream remains in place, nearly a month after it was first issued.
The warning was issued on December 22 and came after routine water samples taken by the Bay of Plenty Regional Council started showing high levels of bacterial contamination.
The contaminated water puts users at risk of contracting infections or illnesses such as gastroenteritis, diarrhoea and vomiting. The sample was taken at the section of the stream near the railway bridge.
Toi Te Ora Public Health Service on-call medical officer of health Dr Jim Miller confirmed the warning was still in place and the cause of contamination had not yet been identified.
He said Rotorua Lakes Council was looking into the reason for elevated contamination levels.
The council's resource management compliance officer Kurt Williams said they were still taking water samples for testing.
"We are unable to say what the reason for the elevated contamination levels is as we're currently taking samples and will be submitting them to laboratories for analysis."
People should avoid areas where stormwater outlets discharge into watercourses, areas with high run-off from intensive agriculture and not swim in streams for up to 48 hours after heavy or prolonged rainfall.