A mystery contaminant in Macandrew Bay has resulted in the Dunedin City Council advising against recreational water use in the area.
Public Health South was notified of high levels of bacteria in the water this week, medical officer of health Dr Marion Poore said.
"At this stage, we are advising against swimming and other recreational activities."
It was the first time Dr Poore had been aware of such a contamination in Macandrew Bay.
The Otago Regional Council, which carried out testing of fresh-water bodies, tested the stream flowing into the bay twice a month.
ORC compliance staff had visited the site in an attempt to locate the source of the contamination but could not pinpoint anything.
However, there was no evidence of sewage contamination, director of resource management Dr Selva Selvarajah said.
Signs had been erected by the DCC informing the public of the bacteria issue.
Dr Poore would work with both organisations until the matter was resolved.
St Clair beach in Dunedin reopened yesterday to swimmers after closing on Thursday because of harmful levels of bacteria in the water.
Retesting showed the bacteria levels were within safe ranges and recreational activities could resume.
Bacteria levels increased when weather reversed the usual sea currents, pushing sewage from Lawyers Head down the coast, rather than northwards.
It was the first time the beach had been closed since December, according to Otago Daily Times records.
