In the laboratory, water samples are pumped through filters, which allow water to pass through but retain bacteria. In the past, we have enumerated fecal coliforms. These are bacteria associated with recent contamination of water with fecal waste from warm-blooded animals, such as humans, birds and dogs. In 2001, we switched to a new group of organisms, the enterococci. These bacteria are also associated with fecal waste, but have been found more closely associated with instances of human illnesses, such as gastroenteritis, following swimming in natural waters.

These filters are placed on microbiological media on Petri plates that encourage the growth of the bacteria of interest but discourage the growth of other microorganisms. Although enterococci are found in fecal waste, they themselves are not harmful to our health. They are useful as indicators of water quality. If enterococci counts are high (>35/100 ml of water), then we would suspect that there might be enough recent fecal contamination of the water to suggest the presence microorganisms that might truly cause illness, such as gastroenteritis or ear infections.

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