Bathers are being urged to avoid the beach off FM Ferretti Street in Birżebbuġa because of a sewage overflow.
The Environmental Health Directorate said it was investigating the source of contamination.
The directorate does not yet know when the site will be safe for swimming again.
Signs about the health risk have been installed on site. When the quality is restored, the signs will be removed.
More information on 2133 7333 or wrau.ehd@gov.mt
Photo: Environmental Health Directorate