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How is beach water tested

Fecal contamination is determined through grabbing and analyzing beach water samples.

Iced samples are taken to a certified local laboratory and processed within 6 hours. Once at the lab, water samples are funneled onto a filter, and the filter is aseptically transferred to a Petri dish where a media is present to encourage bacteria growth. The Petri dishes are then incubated for 24 hours to stimulate growth. If fecal indicator bacteria (E. coli or fecal coliform) were present in the water sample, then bacteria colonies will have grown on the Petri dish. The level of fecal contamination at a beach is determined by the number of colonies present on the Petri dish.

Quality Assurance Project Plan - Minnesota Lake Superior Beach Monitoring Program (10 MB pdf - opens in new window)

NRRI MPCA MDH