Recreational waters are monitored for bacteria using indicator organisms such as enterococci, the indicator of choice for estuarine and marine waters. Enterococci are a group of organisms used to determine the extent of fecal contamination of recreational waters.
Enterococci are a subgroup within the fecal streptococcus group. Enterococci are distinguished by their ability to survive in salt water, and in this respect they more closely mimic many pathogens than do the other indicators. Enterococci are typically more human-specific than the larger fecal streptococcus group. EPA recommends enterococci as the best indicator of health risk in salt water used for recreation and as a useful indicator in fresh water as well.