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Bob Creek E. coli Bacteria

Escherichia coli ( E. coli ), a bacteria, is the EPA recommended indicator of fecal contamination in fresh waters. It is present in high numbers in the gastrointestinal tracts of vertebrate animals and therefore provides a senstive measure of fecal pollution.

The EPA recommended limit of E. coli is 123 CFU ("Colony Forming Units" or cells) per 100 mL for recreational waters. Disease-causing organisms can be carried in fecal-contamination, and the detection of high levels of E. coli indicates that pathogens such as enteroviruses, Norwalk viruses, Coxsakie A and B, Hepatitis A, Shigella spp., and Salmonella spp. may be present.

Typical testing for E. coli cannot not differentiate the source of the contamination(e.g. animal vs. human), since it is present in all warm-blooded mammals.

E. coli is tested at Bob Creek because elevated levels have been seen after large rain storms. A possible source could be a cattle pasture upstream. Other sources could include wildlife (beavers, water birds, etc) or a malfunctioning septic system. E. coli was tested in Bob Creek in 2008-2011. The figure below shows the E. coli numbers compared to the EPA standard. The second figure shows that elevated E. coli levels are usually seen after large rain events. This means that the E. coli is washing off the land and into the water.

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