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Merrimack River Watershed

The Merrimack River is formed in central New Hampshire by the confluence of the Pemigewasset and Winnipesaukee Rivers. The river flows for 115 miles from Franklin, N.H., to the coastal city of Newburyport, Mass. Spanning the two states, the watershed is the fourth largest in New England (over 5,000 square miles). 

The Watershed’s Importance to the Greater Lowell region
The Merrimack River and its watershed is a vital natural resource for all nine communities within the Greater Lowell region, supporting a vast ecosystem, providing drinking water, energy (hydropower), recreational opportunities such as boating and swimming, and enhancing the quality of life for its residents. The City of Lowell and the Town of Tewksbury use the Merrimack River as a direct source of drinking water, after water treatment to ensure that the water is safe for drinking.

Environmental Issues in the Greater Lowell Region
Like most rivers in New England, the Merrimack River absorbs treated waste from both the community and its industrial plants. For many years, people used the river as an open sewer. In the late 1960s, the Merrimack River was considered one of the 10 most polluted waterways in the U.S., and was so polluted that people were unable to swim, boat, fish, or even go near the river. Thanks to concerted effort from residents, the states, and nonprofit organizations, the water is much cleaner, and is now considered Class B waters (fishable and swimmable).

Today, communities within the Greater Lowell region struggle with water quality issues along the river and its tributaries due to stormwater impacts from increasing amounts of impervious surfaces (ground cover in which water cannot pass through, such as asphalt or a roof), and combined sewer overflows (CSOs). A CSO is a sewer system in older cities, in which stormwater and sewage collect in the same pipe and may be discharged untreated, directly to the river during heavy rains. Impervious surfaces directly influence the health of the river by dramatically increasing surface runoff, degrading water quality, increasing water flow rates during storms, causing flooding, and impacting the health of the ecosystem. See Water Quality in the Greater Lowell region for more detail.

Maintenance of the river’s water quality upstream of the Greater Lowell region is critical to ensuring the river’s future use for water supply and recreational purposes. The Merrimack watershed is currently considered the most threatened in the country for loss of private forested land (due to housing pressures in southern New Hampshire), and fourth in possible impacts to water quality, according to the USFS (Forests on the Edge, 2009).

Subwatersheds of the Merrimack River within the Greater Lowell region
While the entire Greater Lowell region falls within the Merrimack watershed, its nine communities share different subwatersheds. Subwatersheds are classified by the U.S. Geological Survey at different, nested scales using the Hydrological Unit Classification (HUC) system. At a HUC8 level, the Greater Lowell region comprises three subwatersheds within the Merrimack River watershed, along with a small portion of the Ipswich River subwatershed.

Each community is listed below, along with its HUC8 subwatersheds:

  • Pepperell: Nashua
  • Dunstable: Nashua, Merrimack
  • Tyngsborough: Merrimack
  • Westford: Concord, Merrimack
  • Chelmsford: Concord, Merrimack
  • Billerica: Concord, Merrimack, and a small portion of the Ipswich River subwatershed
  • Tewksbury: Concord, Merrimack
  • Dracut: Merrimack
  • Lowell: Merrimack

Tributaries of the Merrimack River within the Greater Lowell region
There are several major tributaries (e.g., streams, brooks, or rivers) to the Merrimack. The major tributaries within the Greater Lowell region are:

  • Beaver Brook: Lowell, Billerica, Westford
  • Black Brook: Lowell
  • Concord River: Billerica, Lowell, Chelmsford
  • Nashua River: Pepperell
  • Nissitissit River: Pepperell
  • Stony Brook: Westford