Monitoring Merrimack River Mainstem and Tidal Reaches in Massachusetts to Evaluate Water Quality Conditions, May to September 2020

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The Merrimack River watershed, the 4th largest watershed in New England (Massachusetts Executive Office of Environmental Affairs, 2001), has seen substantial growth and development in recent years.


Location map of the Massachusetts section of the Merrimack River

Map of Merrimack River and locations of USGS/MassDEP water-quality sampling and monitoring stations (Public domain.)

The Massachusetts section of the Merrimack River begins in Tyngsborough, Mass. at the New Hampshire State line and travels roughly eastward to the mouth in the Newburyport and Salisbury area (fig. 1). The Merrimack River represents the public drinking water supply source for several major cities in Massachusetts as well as the receiving water for several Waste-Water Treatment Facilities (WWTFs). Combined Sewer Overflow (CSO) discharges also intermittently affect water-quality conditions during some large storm events. The Merrimack River watershed was ranked as one of the most threatened in the country due to the rapid development of private forested lands (American Rivers, 2016). The Merrimack River also is considered one of the three most important large rivers on the East Coast in its conservation value to migratory river herring and the sixth most important large river for 12 migratory fish species, including a spawning population of endangered shortnose sturgeon. In addition, the Merrimack River watershed supports at least 75 state and federally listed endangered species, numerous pairs of bald eagles, the largest tidal marsh habitat in New England, and a portion of the Atlantic Flyway bird migration route (American Rivers, 2016).

USGS boat crew on Merrimack River, Massachusetts

Two USGS scientists traveling by boat to estuary sampling and monitoring stations, Merrimack River, Massachusetts

(Credit: Jason Sorenson, U.S. Geological Survey, New England Water Science Center. Public domain.)

Water-quality data on the lower Merrimack River are needed to address data gaps, develop further understanding of the impacts attributed to rapid land cover change, stormwater runoff, and tidal exchanges, and to support management initiatives. This field study, in cooperation with the MassDEP, will be conducted from May to September 2020 to characterize water quality and to evaluate approaches for a longer-term monitoring study for the lower Merrimack River.