Charles River Report Card
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Since 1995, U.S. EPA has graded the Lower Charles River Basin—Watertown to Boston—using only E. coli data from water samples collected monthly by CRWA volunteers. Starting in 2019, the grade encompasses all 80 miles of the river and two tributaries, based on data from thirty-nine sampling sites. Grades are being issued for four sections of the Charles River mainstem: the Upper Watershed (Hopkinton to Medfield), the Upper Middle Watershed (Sherborn to Dedham), the Lower Middle Watershed (Newton to Waltham), and the Lower Basin (Watertown to Boston). Two tributaries of the Charles have also been graded: the Stop River in Medfield, and the Muddy River in Boston.
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Water Quality Reports and Data
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CRWA’s Volunteer Monthly Monitoring (VMM) program analyzes river samples once each month at 35 locations in the watershed for Escherichia coli (E. coli) bacteria, an indicator of human health risks. Water is also analyzed every 3 months at a subset of 12 sites for additional water quality parameters such as nitrogen, phosphorus, total suspended solids, and plant pigments. This robust dataset drives allows us to analyze trends over time and space.
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Flagging Program
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CRWA’s Flagging program notifies boaters of current river health during peak recreational season from Watertown to Boston. Blue (safe for boating) and red (not safe for boating) flags are updated hourly on our website and social media, and physical flags are flown at 12 boathouses on the river. Red flags are flown when: CRWA’s models estimate bacteria levels that exceed the state boating standard; a combined sewer outflow occurs (spurring a 48 hour warning); and/or the appearance of a cyanobacteria bloom.
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