Bacteria and Health Safety

Is the river safe for boating or swimming? OARS is attempting to answer this with its E. coli bacteria (an indicator bacteria) monitoring program. Bacteria and other pathogens can enter the rivers from leaking sewers or septic systems, storm-water runoff, or wildlife or dog waste. The EPA has linked high E. coli levels in swimming water to high rates of gastro-intestinal illness.

This year we began monitoring levels of pollution from these sources to evaluate the safety of our rivers for swimming and recreation. Between June and September, water samples were collected weekly by volunteers at 6 locations throughout the watershed. Samples were analyzed in a lab and bacteria counts were recorded as Colony Forming Units.

The EPA has established swimming safety thresholds of 235 colony-forming-units/100mL for single samples or 126 cfu/100mL for seasonal geo-mean averages. We hope to use our sampling results to identify which sections of the river are safe for swimming and to identify pollution sources that need to be addressed.

We need volunteers, especially those who live near Ashland, Hudson, or Lowell, to help us collect samples in 2020. If you are interested, please contact

Results from June 17 - September 23, 2019

Check out our map of sampling locations with color-coded 2019 results.