Swimmers are being advised to take extra precautions at the Marina Way beach in Penticton after high levels of E. coli were found in the waters there.
Testing on May 18 and a retest on May 22 found levels more than twice the acceptable limit.
An advisory has been posted by the city to warn swimmers.
The possibility of illness increases with the bacteria level. Authorities do not believe anyone will become sick, but are still asking swimmers to take a number of precautions.
Swimmers are asked to avoid swallowing lake water, to wash their hands before handling food and to not swim with an open cut or if already ill.
Under conditions where bacteria may be washed into the water from the shore, such as strong northern winds or if the lake level is high, authorities suggest not swimming.
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