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Microbial Assessment Category (MAC)

The Microbial Assessment Category (MAC) is calculated from water samples collected weekly over five summers (usually from November to March) that characterise potential microbiological contamination at a particular site. The samples are tested for bacteria that are indicators of faecal contamination and thus of the presence of disease-causing micro-organisms. The indicator bacteria used are Escherichia coli (E. coli) in fresh water and enterococci in coastal waters. The concentration of the bacteria is converted into categories from A (no risk level of bacterial infection) to D (significant risk of bacterial infection).