The Otago Regional Council advised last week it had to reinstall signs at the two swimming areas after levels of cyanobacteria, or blue-green algae, and E. coli, respectively, had elevated beyond the levels considered safe for swimming.
ORC environmental scientist Rachel Ozanne said this week's water quality testing from Lake Hayes showed cyanobacteria levels had reduced to a suitable level for contact recreation, but under government guidelines, the biovolumes had to return to a safe level for two consecutive weeks before water was deemed safe for swimming.
However, swimmers were able to return to Frankton Bay.
Signs advising against swimming the Manuherikia River at Shaky Bridge, in Alexandra, were also removed on Wednesday, after water sampling. Macandrew Bay, in Dunedin, returned an elevated level of Enterococci last week, due to rainfall.
"With calmer weather this week, the bacteria has reduced to a minimal level and is suitable for swimming," Ms Ozanne said.
