The Office of Environmental Health and Pollution Regulation, with assistance from Guernsey Water, has been investigating the incident and stated that the source has been identified.
But the exact nature of the pollution and its source have not been made public.
The beaches will remain closed until the area is deemed clean again.
Warning signs have been put out at the entrances to the west coast beaches as a precaution to keep walkers and pets safe, while remedial action takes place to prevent the recurrence of this polluting incident.
Testing has been arranged to verify its effectiveness and the signs will be removed once testing shows the area is clear of the pollutant.
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