Swimmers are being warned to not enter the water at The Pond in Safety Bay.
Recent water quality tests have produced "elevated results", but the City of Rockingham has not revealed what was found in the tests.
The City has put up warning signs around the area which state swimming in the water may cause "ill effects to humans and animals".
"The signs will be removed once further water results show the water quality has returned to safe swimming levels," the City of Rockingham wrote on their Facebook.
Perth to Bunbury train service returns
Missing woman found safe and well
Community fed up with teenage hoons terrorising Halls Head oval
Southern suburbs electrician claims $1.8 million Lotto win
Works continue on Pinjarra's Munday Avenue extension
Halls Head support worker charged with historic child sex offences
Severe thunderstorm warning cancelled for Mandurah, Bunbury
Fortnightly red bin collections to remain in the City of Rockingham after council rejects motion
Rate rises on the way for Rockingham, Mandurah ratepayers