Merrimack River Watershed

The watershed is a recreational resource for nearly 200 communities and 2.6 million people and is the primary drinking water source for about 550,000 people in Massachusetts and New Hampshire. The vast two-state watershed covers 5,010 square miles and is home to a variety of sensitive species and habitats.

EPA created this interactive StoryMap to bring together important geospatial data about the Merrimack watershed and to serve as a collaboration platform. With many strategic partners working to protect the watershed, this product offers information to help visualize some of the watershed’s greatest challenges and attributes, as well as helpful resources for water monitoring coordinators working across the watershed.

This interactive map has information about water uses in the watershed. It includes the wastewater treatment facilities, combined sewer discharges to the watershed, and communities that take drinking water from the river. It also provides an overview of the watershed and major tributaries to the Merrimack River.

Click on the two arrows (top right) to expand the map, the search button (top left) to find an address or place, zoom in/out buttons (bottom right), or the legend button (bottom left) to view the map legend:

Extreme weather in a changing climate has caused major flooding in the Merrimack River watershed and threatens water quality, critical infrastructure and property. These maps provide visual information on flooding scenarios, storm surge inundation and sea level rise. This map focuses on Newburyport, Massachusetts, a coastal community that has experienced major flooding over the last few years. Note that these national data layers are available for other areas of the watershed by zooming to different locations.  

Flood hazard zones are based on FEMA’s Flood Insurance Rate Map. These special flood hazard areas are defined as the area that will be inundated by the flood event having a 1-percent chance of being equaled or exceeded in any given year. The 1-percent annual chance flood is also referred to as the base flood or 100-year flood. The 0.2-percent annual chance flood is equivalent to the 500-year flood.

NOAA National Hurricane Center Storm Surge Inundation Model (Cat 1-4):

The National Hurricane Center uses the hydrodynamic Sea, Lake and Overland Surges from Hurricanes (SLOSH) model to simulate the water inundation (water height and area) during storms. Click on the 4 tabs below to see what this model predicts for the four different hurricane categories in Saffir-Simpson scales.

NOAA Sea Level Rise:

The  NOAA Sea Level Rise web mapping tool  (opens in a new tab) is used to visualize community-level impacts from coastal flooding and/or sea level rise. Photo simulations of how future flooding might impact local landmarks are also provided, as well as data related to water depth, connectivity, flood frequency, socio-economic vulnerability, wetland loss and migration, and mapping confidence. You can use the bar on the left to adjust the sea level rise you are interested in evaluating.

According to a report on " Global and Regional Sea Level Rise Scenarios for the United States "  exit  published by the U.S. Sea Level Rise and Coastal Flood Hazard Scenarios and Tools Interagency Task Force in February 2022, in the Northeastern United States, the intermediate scenario calls for 1.41 ft of relative sea level rise in 2050. This height is bounded by NOAA’s +1ft and +2ft polygons. For mapping conditions in 2050: the +1ft polygon is very likely to be exceeded, and the sea is very likely to remain below +2ft which can be used as an upper height. Conditions are most likely to correspond with the Intermediate-Low, Intermediate or Intermediate-High scenario. The range of the three intermediate scenarios is bounded by NOAA’s +2ft and +6ft polygons. For mapping in this region, 6 feet of relative sea level rise can be used as an upper, unlikely to be exceeded height for 2100.

The Merrimack River flows through some of the most highly developed areas in New England, including New Hampshire’s three largest cities and three of Massachusetts’ famous historic mill towns, as well as the urbanized areas surrounding those cities as the river flows from the White Mountains to the Atlantic Ocean.  On its way, it picks up pollutants like bacteria, algae-stimulating nutrients, metals and other harmful chemicals. 

Control of pollution discharges from wastewater treatment plants and industry have made it possible to swim and fish in parts of the river where such uses were unthinkable 60 years ago.  Yet, more work needs to be done to open the river and its tributaries up to all the uses New England residents expect from it.

The Land Use and Assessed Waters web mapping application displays assessed water features from   EPA’s ATTAINS Database  , as well as land use classifications and impervious surfaces. It shows those waters that are polluted and the pollutants that need to be reduced.

In New Hampshire all waters are listed as polluted for mercury as a result of a statewide fish consumption advisory, primarily due to atmospheric deposition, so the map only shows waters that are polluted for any cause in addition to mercury. For current NH water quality data see their  2018 Surface Water Quality Assessment viewer .  exit 

Runoff from developed areas is the largest source of water pollution in New England, due to the region’s high population, building and vehicle density, and the large cities and urban areas along its Atlantic coast and rivers.  Rain and snow melt runoff from hard surfaces like buildings, roads and parking lots, sometimes called “impervious surfaces,” wash accumulated pollutants off those surfaces and into lakes and rivers.  Water quality tends to be worse the more impervious surfaces there are, as hard surfaces prevent runoff from soaking into the ground where it can be filtered by the soil.  Much of that runoff is not treated in any other way to remove pollutants before it enters water bodies.  Recent advances in pollution treatment, called stormwater best management practices, have increasingly allowed cities and towns to treat runoff in their neighborhoods before it enters water bodies, and reduce the amount of impervious surfaces.

Large cities with high population densities are required to clean up stormwater pollution through permits in the Municipal Separate Storm Sewer System (MS4) program, although the same type of pollution outside the boundaries of those high-density areas is not regulated.  The boundaries of these “urbanized areas” are defined by the most recent U.S. census.

In certain communities, sewer systems are built to allow stormwater and sanitary sewage to mix when large rain storms occur. When this happens Combined Sewer Outfalls (CSOs) overwhelm the sewer system, resulting in discharges to rivers of untreated sanitary sewage mixed with stormwater. This map helps visualize some of the water quality challenges in the lower Merrimack, highlighting the communities served by the Greater Lawrence Sanitary District (GLSD) and information about CSO locations.

Long-term plans for updating New England’s aging infrastructure are required by EPA enforcement orders at all of the CSO communities (including GLSD) on the Merrimack. Until this work is complete, CSOs will continue to degrade water quality.

Land conservation in the Merrimack River is critically important for protecting water quality and the ecosystem.

Through development, land is converted to impervious cover, impacting water quality in neighboring streams and rivers. The 2009 U.S. Forest Service report  Private Forests, Public Benefits: Forests on the Edge, Stein et al .  exit   ranked the Merrimack River watershed at the top of its list in terms of total acreage of private forest projected to experience increased housing density. The Merrimack was also listed as the fourth most threatened watershed in the country based on changes in water quality, due to potential conversion of private forested lands to housing. For this reason, the Merrimack Conservation Partnership was established in 2012 to help promote land conservation. 

The Protected & Conservation Focus Areas web mapping application showcases the  Protected Areas Database  (PAD) and the conservation focus areas from the  Merrimack Conservation Partnership Conservation Plan .  exit   View the technical report .  exit 

Water quality monitoring is a crucial aspect to protecting and understanding water resources. Under the Clean Water Act, state, tribal and federal agencies monitor lakes, streams, rivers and other types of water bodies to determine water quality condition. In addition, many nongovernmental watershed associations, nonprofits and academic organizations conduct their own water quality monitoring to answer locally driven questions. The data generated from these monitoring activities help water resource managers know where pollution problems exist, where to focus pollution control resources and where progress has been made. 

The U.S. Environmental Protection Agency (EPA) and partners have been working to improve the ease with which organizations large and small can store their water quality monitoring data in the  Water Quality Portal . Once there, data become accessible to scientists, government policy makers, and the public in a permanent archive. Below are available tools and resources that help organizations contribute, view, share and interact with data in the Portal.

How’s My Waterway provides information about the condition of local waters based on data that states, federal, tribal, local agencies and others have provided to EPA. Water quality information is displayed on 3 scales in How’s My Waterway: community, state and national. More recent or more detailed water information may exist that is not yet available through EPA databases or other sources. Check out the  How's My Waterway Fact Sheet. 

 How’s My Waterway provides a  data page  which lists the sources of data displayed as well as where this data shows up throughout the tool. The data page can be found at the top of any page in How’s My Waterway.

If you're an educator that's looking for lesson plans, webinars, and other educational materials you can consult EPA's  How's My Waterway resources for educators .

This dashboard summarizes the water quality monitoring data from the Water Quality Portal for the Merrimack River Watershed going back to 1972.  The dashboard highlights the sampling efforts in the watershed by various organizations and provides analysis capabilities that can be used to evaluate water quality conditions.  Users can look at trends over time or compare sampling stations and characteristics in a variety of ways by a variety of metrics. Source Data Description: Water Quality Portal (via Web Services) Data Refresh Schedule: Quarterly Audience or Use Cases: The dashboard provides increased capacity for data analysis and expand data sharing among state-level and community-based monitoring groups by providing local access to their water quality data, as well as data from other organizations to augment their own water quality data for data analysis and identifying opportunities to improve conditions.  The dashboard was designed as a tool specific to state-level and local community-based monitoring group data access and analysis needs to complement the more generalize approach of the EPA’s How’s My Waterway.

Government agencies and nonprofit environmental groups can share their data publicly through the national   Water Quality Portal  by submitting data to EPA’s  Water Quality Exchange   (WQX).  From the Portal, data can be integrated into a variety of viewers, data analytical tools, portals and data assessment products, like   How’s My Waterway , the  Merrimack River Watershed Dashboard , and the  WQP Tools for Automated Analysis  (TADA).   The result is greater data accessibility for the public and increased utility by decisionmakers. The  MassBays National Estuary Partnership   exit  developed MassWateR to assist nonprofit environmental groups in preparing and submitting their data to WQX. The package and guiding materials are available on the  MassBays Github site .    exit 

Nonprofit / Nongovernmental

 Merrimack River Watershed Council   exit  

 Nashua River Watershed Association    exit  

 Souhegan River Watershed Association   exit  

 Upper Merrimack Watershed Association   exit  

 OARS    exit 

 MassAudubon   exit 

 Groundwork Lawrence   exit 

 Essex County Greenbelt   exit 

Town, State, and Federal Agencies

 Merrimack Valley Planning Commission    exit  

 Merrimack Valley Stormwater Collaborative   exit  

 Lowell Waterwater Utility   exit 

 Haverhill Wastewater Treatment Plant   exit  

 Pennichuck Water Works   exit 

 Greater Lawrence Sanitary District   exit 

 New England Interstate Water Pollution Control Commission (NEIWPCC)   exit  

 Massachusetts Dept of Environmental Protection (DEP)   exit 

 Massachusetts Division of Marine Fisheries (DMF)   exit  

 Massachusetts Division of Fisheries and Wildlife (DFW)   exit 

 New Hampshire Department of Environmental Services   exit  

 New Hampshire Fish and Game Department   exit 

 US Army Corps of Engineers (ACOE) 

 US Geological Survey (USGS) 

 US Environmental Protection Agency (EPA) 

 NOAA Fisheries 

Universities

 UMass Lowell   exit  

 Northern Essex Community College   exit 

 Boston University   exit