Testing Methods

The monitoring season is typically from late May to October. Each partner group monitors at different intervals and begins at different points in the season. 

Volunteers are trained annually on proper sampling techniques to collect a representative sample and avoid contamination. Most groups also collect Quality Control samples to verify sampling, handling, and lab processing techniques. Most samples are lab analyzed using the Colilert system from IDEXX. Results are posted to this site within 24 hours after the sample was taken.


The data will show bacteria levels for each sampling date and also whether or not it was a wet weather event. Wet weather is often defined as any day in which more than 0.1 inch of rain fell within the 48 hours preceding sample collection. Some groups may define this differently. Use the wet weather information to better understand if rain is a factor leading to a site being less clean for recreation.

Swimming is defined as any recreation or other water use in which there is prolonged and intimate contact with the water with a significant risk of ingestion of water. These include, but are not limited to, wading, swimming, diving, surfing and water skiing.

Boating is defined as any recreation or other water use in which contact with the water is either incidental or accidental. These include but are not limited to fishing, including human consumption of fish, boating and limited contact incident to shoreline activities.

CRC’s Water Testing Laboratory

In 2007, CRC launched the volunteer water quality monitoring program at a handful of riverside sites. Our laboratory opened in 2009 and now processes bacteria samples from over 80 locations in Massachusetts and Vermont every swimming and boating season. Our lab is a central site where watershed organizations can bring water samples, have them processed, and quickly get critical water quality information posted for the public and decision-makers. Organizations and individuals looking to get samples tested are welcome to contact the lab directly for availability.