Indicator organisms themselves are not necessarily pathogenic but their presence "indicates" or suggests recent contamination by human sewage or other waste which may result in human illness. Sources of contamination include storm water runoff, sewage overflows and feces from wild and domestic animals.
The currently used bacterial indicators for recreational waters include total coliform, fecal coliform and enterococcus. Total coliform is a group of bacteria found in the intestinal tract of warm-blooded animals but some may also occur naturally in the environment. Fecal coliform is a sub-group of total coliform and serves as a more specific indicator for human and animal waste contamination. Enterococci is present in the intestines of all warm blooded animals and because it survives longer than fecal coliforms in natural waters, enterococcus is a more reliable measure of water quality.