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Boston Harbor's Tributary Rivers: Patterns of River Bacteria


Average bacteria levels in the Charles have decreased 80%, while the Mystic and Neponset Rivers have shown little or no improvement. The Mystic and Neponset are more affected by stormwater than by CSO. Improved pumping and hydraulic capacity at DITP greatly decreased discharges from Charles River CSOs. Also, communities along the Charles have been working to clean up stormwater discharges. Although there have been local improvements at the mouth of the Mystic River near MWRA’s Somerville Marginal CSO Treatment Facility, the overall average water quality in the Mystic has changed very little.
While CSOs have been eliminated in the Neponset, stormwater still contaminates that river. (Lines above bars indicate margin of error.)

Sailboats on the Charles River







In the Charles, improvement in water quality over the past ten years has been dramatic; fecal coliform counts (geometric mean) fell by over five-fold. Although the Mystic River shows slight improvement over this period, the Mystic and Alewife Brook are still plagued with contaminated stormwater and CSOs. Implementation of MWRA’s CSO Plan will control CSOs, but stormwater is a major source of bacteria. Although closing CSOs and better CSO treatment at MWRA facilities has reduced inputs of bacteria to the Neponset, stormwater sources are so much larger than were CSOs that water quality in the lower Neponset has remained about the same since monitoring began.

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