Monitoring and Studies


To ensure that decisions affecting the rivers are based on reliable science and that the changes in management—like wastewater treatment plant upgrades—are effective in improving the rivers' health, OARS monitors conditions on the rivers.

Water Quality, Streamflow, and Habitat (1992–present): In 1992, OARS started a testing water quality to evaluate the impact of wastewater treatment plant upgrades completed in the late 1980s. OARS volunteers have tested water quality every summer since 1992. Today OARS monitors at mainstem and tributary sites from the Westborough and Saxonville to Lowell. In 2020 OARS also monitored water quality in Hop Brook, Sudbury.

Data are collected under OARS' approved Quality Assurance Program Plan (QAPP) and may be used in making regulatory decisions. OARS' data are submitted to the Mass DEP and are used in their "Integrated List of Waters" report. OARS' annual Water Quality Reports are available on the Water Quality Reports page. Collecting data is not enough! Read more about what the data mean and how OARS' Stream Health Index is calculated to assess overall river health.

Bacteria Monitoring for Health and Safety (2019–present): In 2019 OARS began monitoring levels of E. coli to evaluate the safety of our rivers for swimming and recreation. We began a source-tracking project in Lowell in 2020 to find the sources of bacteria pollution in the lower Concord River.

OARS Conductivity and Chloride Surveys (2022–present): In 2018, OARS began monitoring chloride levels and in-situ conductivity to directly measure salt concentrations in our waterways, as they associated with adverse effects in our rivers.

Trout Streams and Temperature (2012–present): In 2012/2013 OARS collaborated with the Greater Boston Chapter of Trout Unlimited (GBTU), Sudbury Valley Trustees, and USGS Conte Anadromous Fish Labs. Building on the successful efforts of GBTU, the Sudbury Conservation Commission, and MA Fish and Wildlife to identify small trout streams in Sudbury, the project looked at conditions in Cranberry and Trout Brooks to identify opportunities to protect these cold-water fisheries. Temperature monitoring continues on these streams.

River Continuity: In the spring of 2010, OARS volunteers surveyed over 70 culverts and bridges in the Nashoba Brook sub-watershed to assess whether they pose barriers to the passage of fish and wildlife. In 2013, as part of the Trout Stream project, OARS volunteers surveyed additional culverts and bridges on several small streams in Hudson, Marlborough, and Sudbury.

Mapping Invasive Aquatic Plants: OARS surveyed invasive aquatic plants on the Sudbury, Assabet, and Concord Rivers to map known invasives, find new infestations, and prioritize and track the progress of water chestnut pulling. In 2013, 2014 and 2016, OARS surveyed all of the mainstem rivers (Sudbury, Assabet, and Concord) for water chestnut as part of the SuAsCo CISMA water chestnut control effort funded by the Nyanza Restoration Fund. In 2018 OARS piloted a project to use drones to survey water chestnut. More about managing water chestnut in the basin. OARS chairs the Aquatic Invasive Management Subcommittee of CISMA which meets regularly to share experiences and information.

Plant biomass (2005–present): In August each summer, OARS assesses the mass of aquatic plants growing in the river. This is a long-term effort to measure changes in the aquatic plant biomass in response to the major upgrades to the watershed's wastewater treatment plants completed in 2012.

Endocrine Disrupting Chemicals: In 2010, OARS collaborated with the University of Massachusetts' Professor Arcaro to study the effect of endocrine disrupting chemicals in the Assabet River.