Rahway River, Rahway Valley Sewerage Authority, NJ

Enterococcus is a group of bacteria that normally lives in the intestines of people and animals. When it shows up at higher levels in the water, it can be a sign that sewage or other fecal contamination has reached that area.

It is used as an indicator organism, which means it helps flag the chance of sewage-related contamination without measuring every harmful thing directly. That makes it a useful way to track bacteria-based water quality conditions across many sites over time.

Lower numbers usually mean cleaner conditions for recreation. Higher numbers suggest elevated or high contamination levels, especially after rain.

MPN stands for Most Probable Number, a standard lab estimate of how much bacteria is present in a water sample. On this site, 35 MPN / 100 mL is the main reference point used to compare lower contamination levels with elevated results.

This is still only one part of water quality. These readings do not measure every form of pollution, and a single sample only captures one moment in time.