It is the second summer high concentrations of E.coli bacteria have been recorded in the river at Waipiata.
In late December and early January E.coli levels soared above ''action'' levels, making it unsafe for swimming and the Otago Regional Council and Public Health South issued warnings for people to keep out of the water.
E.coli then dropped to ''alert'' levels, making it safer but people were urged to hold off swimming in the area.
The levels spiked again to ''action'' level early this month, although they have since dropped back to below ''alert'' levels.
Throughout the summer the Otago Regional Council has been closely monitoring the level of contamination and investigating possible causes.
It had installed three additional water quality recording sites upstream of the permanent site at Waipiata and staff regularly visited to see they could determine the source.
Council engineering, hazards, and science director Gavin Palmer said the latest spike in E.coli happened when there had been no rain, which added to the picture, but a clear cause still had not been found.
The most recent tests on February 10 found two of three additional sites were below the ''alert'' level while one was above ''alert'' but below ''action'' level.
As the council was continuing to struggle to find a potential source of the contamination it was reviewing its plan of attack this week, he said.
He urged people to continue to be ''prudent'' around decisions to swim in the affected area between Waipiata township and Creamery Rd bridge.
