2023 Rivers Report Card for the Sudbury, Assabet, and Concord rivers

Our scientifically rigorous rivers report card informs you of the health of the Sudbury, Assabet, and Concord river system. Under the Clean Water Act, our three rivers should be “fishable and swimmable,” an as-yet unrealized goal.

Our Rivers Report Card compares 18 indicators of river health to scientifically derived thresholds, (see Methods Report online).. These individual indicators are combined to calculate scores for each of the five values developed with watershed stakeholders—Water Quality, Streamflow, Scenery, Habitat, and Recreation—for each river’s upper and lower segments.

The scores for these five values were then combined into an Overall Health score for each river segment. The overall grade for the complete river system is the average of these six river segment scores, weighted by area.

Grades are displayed using the following health scale:

The Sudbury, Assabet, and Concord Rivers Report card
Many trails and access points were added, but alternating droughts and floods improved groundwater level but impaired water quality. The grading now includes bacteria, aquatic connectivity based on the number of dams, and water quality and scenery in the Upper Sudbury. Each river is divided into upper and lower sections. The grades of all sections are reflected in the final grade for the river system.,/td>
Upper Sudbury River
The grade improved with new recreation trails added and good water quality despite some bacteria pollution. Fish cannot be eaten due to sediment contaminated by mercury from the Nyanza Superfund site. Old mills and water supply dams obstruct the movement of fish and boaters. Water control at water supply dams alters the natural stream flow. Streamflow and groundwater improved during the years with heavy precipitation.
Lower Sudbury River
The grade is unchanged. It has the highest scenic quality, minimal wastewater discharge, low bacteria levels, and is very accessible. No dams block fish or boaters. The water quality grade dropped due to increased phosphorus and falling dissolved oxygen. No fish should be eaten due to mercury contamination from upstream. The natural streamflow is altered at water supply dams upstream. This is the longest Wild & Scenic River segment.
Upper Assabet River
Improvements in recreation trails and river access raised the grade. However, old mill dams still obstruct the movement of fish and boaters. Wastewater treatment plant discharges continued high nitrogen levels, but phosphorus pollution was reduced. Groundwater level improved, reflecting some years with heavy precipitation. Floating biomass increased in one impoundment and reduced in another and was worse in drought years.
Lower Assabet River
The overall grade is unchanged. The section’s extensive trail networks and new access points raised those scores to A+. The alternating drought and flood years lowered the phosphorus grade; nutrients from wastewater still have an impact. Floating biomass and groundwater level improved somewhat but were worse during the droughts. The many old mill dams obstruct the movement of fish and boaters.
Upper Concord River
This section achieved the highest grade for recreation due to new access points and trails, no dams blocking fish or boating, and is the section most suitable for swimming. It also has significant scenery and cultural resources. Fish are not generally edible due to lingering mercury contamination from the Superfund site on the Upper Sudbury.
Lower Concord River
The overall grade is unchanged. Upstream dams, flow manipulation, and urban land use impact this section. However, recent investment in riverfront trails upgraded that indicator from D+ to B+. The section boundary was corrected, downgrading the passability grade due to an additional dam. Water quality remains good, and fish edibility remains at a C, the state-wide advisory level.


This Report Card was developed by OARS in partnership with the University of Maryland Center for Environmental Science and with the support of the Massachusetts Environmental Trust, The Sudbury Foundation, The Fleetwing Charitable Foundation Trust, the Sudbury, Assabet, & Concord Wild & Scenic River Stewardship Council, in-kind contributions from the National Park Service and US Fish & Wildlife Service, and the participation of many stakeholders and volunteers.


Visit the EcoHealth Report Card Site For Full Report Details
Download Rivers Report Card PDF

Five-step process
Stakeholder workshops
Indicators of river health
Methods documentation