Water Quality

The main environmental problems impacting the Merrimack River water quality in the Greater Lowell region are:


The Merrimack River water quality matters greatly, as the Merrimack is used as a public drinking water supply for four communities, including the City of Lowell and Town of Tewksbury. The Town of Billerica draws its drinking water from the Concord River, a tributary to the Merrimack

The communities within the Greater Lowell region reside along the lower portion of the Merrimack River, which played an important role in the region’s industrialization. Early in the 20th century, many of the textile mills relied on the River as a source of water power to run the mills. During this time period, the mills discharged waste into the river causing the river to become one of the 10 most polluted in the country.

In 1967, the condition of the river water was classified as B or C waters, indicating it was suitable for swimming and fishing. However, many portions of the waterway were considered to be class D, which is the lowest classification and indicates the water was not suitable for recreational contact (Commonwealth of Massachusetts, 1967). Even today, some vestiges of the area’s industrial past remain, including hazardous waste sites, junkyards, and abandoned properties that can negatively impact water quality. 

Following passage of the Clean Water Act in 1972, point source pollution from factories was reduced and the river’s water quality dramatically improved. New treatment technologies and permit requirements reduced pathogens (primarily bacteria) and nutrient concentrations (phosphorus and nitrates-nitrogen) (DEP, MRWC).

Today, the river water is classified primarily as B, meaning that it is fishable, swimmable, and boatable, but the stretch of river within Massachusetts is still considered non-supporting for Class B waters (EOEEA). Pathogens are the main water quality problem, stemming from the Combined Sewer Overflows (CSOs) in Lowell, Nashua, N.H., and Manchester, N.H., along with polluted runoff. Public health and recreational enjoyment of the river is impacted by high bacteria levels.


Pathogens are measured by using the common bacterium E. coli, whose presence indicates that water may be contaminated by human or animal wastes. The pathogen levels are measured against a state standard. The risk of getting sick increases as the number of bacterial colonies increases above the standard. The Merrimack River Watershed Council (MRWC) analyzed water quality data from 2008 to 2012 and found that several areas showed improvement in the average count of E. coli bacteria over the last four years, including Tyngsborough and Lowell. In 2013, the City of Lowell had no days that were considered unsafe for swimming (source: City of Lowell Recreation Department).


Too many nutrients can impact water quality by causing excess algal growth which may kill fish. Urban areas and agricultural areas contribute phosphorus or nitrates, promoting the growth of algae and reducing dissolved oxygen, which is detrimental to aquatic life. Excessive phosphorus comes from older wastewater treatment plants (which do not have tertiary treatment to breakdown phosphorus), combined sewer overflows, polluted runoff, runoff from lawn fertilization, animal waste, and industrial cleaning operations. Excessive nitrate comes from these sources as well and from failing septic systems. In freshwater, controlling phosphates can prevents algal growth.

The greatest contributors of phosphorus to the Merrimack River come from municipal wastewater (60%), and runoff from developed lands (21%) (Gulf of Maine Council on the Marine Environment, 2012). The greatest contributors of nitrates along the Merrimack River are municipal wastewater (38%), runoff from developed lands (29%), and atmospheric deposition from midwestern coal-fired plants (25%). MRWC data from 2010 for the Greater Lowell region shows that overall, phosphorous levels are below EPA guidelines. 

Impervious Surfaces

As development increased in the Greater Lowell area, parking lots and other impervious surfaces increased as well. These impervious surfaces impact rivers through:

  • Increased pollutants from stormwater runoff (oil, grease, brake fluid, animal waste, road salt);
  • Thermal stress (heat from impervious surfaces);
  • Reduction in water quantity; and
  • Flashiness (i.e., changes in river flow speed), leading to bank erosion.

The increase in impervious surfaces has also led to flooding, a key concern of many residents living along the Merrimack River, Concord River and Shawsheen River. When it rains or snows, the water has no place to go but into the storm drains and eventually into the Merrimack River and its tributaries.

As the percentage of impervious surfaces increases, water quality and wildlife diversity and abundance suffer. The latest research shows that both water quality and ecology are degraded when impervious cover is above 5% to 7% (Schiff and Benoit, 2007). The most important areas to protect are the lands bordering the river, or river buffers. Once degraded, river water quality and its ecology are difficult to restore. This is why it is much cheaper to maintain clean water through land protection than with water treatment. Research indicates that for every dollar spent on land protection, $27 are saved on water treatment costs (Ernst et al., 2004).

Forested Area

Water quality within the Greater Lowell region also depends on impacts upstream. Specifically, the forests in New Hampshire help clean the Merrimack River water by absorbing nutrient and sediment runoff before it can reach the river. The runoff also infiltrates the forest soil, cooling the water before it reaches the river. The U.S. Forest Service considers the Merrimack River to be the most threatened in the country for loss of private forested lands (USFS, 2009). Due to this threat, the watershed is considered to be the fourth most threatened in the country for impacts to water quality.

Climate Change

Climate change is projected to increase the frequency of flooding in New England’s rivers. Increased rainfall will lead to increased runoff, and incidents of both flooding and erosion (NOAA, 2011). An additional 32% to 24% increase in total runoff is projected for the U.S. Atlantic Coast by 2100 due to climate change impacts.