The presence of Escherichia coli (E. coli) in surface waters is often attributed to fecal contamination from agricultural and urban/residential areas (human sewage and non-human wastes, such as wastes from birds and other wildlife). However, variation in E.coli concentrations from site to site and in contribution of agricultural vs. human sources are not readily understood. In addition, E.coli concentrations at a particular site may vary depending on the baseline level already in the river/lake water and sediments. The concentration of
E. coli in surface water depends for the most part on the runoff from various sources of contamination.
E. coli as an Indicator Organism
To help maintain water that is safe for swimming, routine monitoring for enteropathogens is necessary, but are difficult to detect. An indicator organism, such as E.coli, is used to determine fecal contamination. The presence of E.coli, a normally nonpathogenic intestinal organism of warm blooded animals, is easy to test for and is relatively more abundant than the enteropathogens thus leaving a safety margin for the detection of disease causing organisms.