Bathers are being urged to avoid St George's Bay in St Julian's after the health authorities detected EColi in the water.
In a statement on Monday, the Environmental Health Directorate within the Superintendence of Public Health said that until further notice, bathing was "not recommended due to the presence of microbiological EColi contamination affecting the bathing water quality and presenting a risk to bathers’ health".
The authorities have not yet determined the source of contamination.
Once the water quality is restored, signs asking bathers not to swim there will be removed.
More information on 2133 7333 or wrau.ehd@gov.mt