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Recent water quality samples taken by the Otago Regional Council (ORC) show high levels of E. coli in Lake Hayes, prompting the council to warn people from swimming in the lake until further testing is done.
ORC resource science manager Dean Olsen said several factors could have an effect on the bacteria levels including recent rainfall, water flow, bird activity, stock in waterways or even whether it is a cloudy or sunny day.
"ORC staff are carrying out further water quality testing this week to determine the cause of the E.coli contamination and whether an advisory against swimming in the area is required. The results of this testing should be available by Wednesday.
People that are considering swimming the lake should hold off until further testing is conducted, he said.
Recreational swimming areas with less than 260 E.coli/100ml should be considered safe according to the Government's water quality guidelines, Dr Olsen said.
Areas that have more than 550 E.coli/100ml are considered as posing a health risk, he said.
"ORC’s most recent sampling in the area showed E.coli levels at 921/100ml."
To find out when the water is safe to swim in, contact the ORC or visit www.orc.govt.nz