Our Estuaries Story…

Our estuaries have declined due to stress and are losing resilience to sustain themselves in the face of growing pressures. There are a number of contributing factors to consider; some are due to human activity while others are the result of natural processes beyond our immediate control. We must continue to work collaboratively to make our estuaries more resilient to the changes they are experiencing now, and those to come. To explore what makes our estuaries complex and interesting places along with data from our 23 indicators on the health of the Great Bay and Hampton-Seabrook estuaries, scroll down to view more on the pressures facing our system, the conditions of critical resources and water quality, and our management/social responses to these issues.


Resilience: The capacity of an ecosystem to absorb repeated disturbances or shocks and adapt to change without continually degrading and fundamentally switching to an alternative stable state.

Climate Change

Driving warming waters, sea-level rise, more extreme storms, coastal acidification, and more.

Population Growth

Increasing populations impact our environment in many ways including demand for resources, loss of open space, and increased pollution.

Land Use

Changes in the natural landscape for commercial, residential, and industrial purposes impact our environment. How we make those changes makes all the difference.

The ecosystem stressors above and others will continue. Focusing on resilience means pro-actively looking for ways to strengthen our ecosystem so that, when these stressors occur, our estuaries are better able to resist and recover from disturbance. Learn more in “The Big Picture.”

To help monitor the changes and stresses in the estuary, the Partnership collects over 1 million data points annually that we combine into a series of indicators that are organized into Pressure, Condition and Response.


Pressure indicators measure some of the key human stresses on our estuaries.

  • Impervious Surfaces
    In 2015, 5.6% of the land area of the Piscataqua Region watershed was covered by impervious surfaces. This is an increase of 1,257 acres of impervious cover or 0.2% of the land area since 2010.
  • Total Suspended Solids
    Suspended solids at Adams Point have increased since 1989, but they have decreased at the Great Bay Station since 2002.
  • Nutrient Loading
    Significant reductions in point source nitrogen loading have and are continuing to occur at municipal wastewater treatment facilities. Non-point source loading has decreased, but low rainfall is a contributing factor.


Condition indicators measure the current state of the conditions in our estuaries.

  • Nutrient Concentration
    Total nitrogen decreased at Adams Point but increased at the Chapman’s Landing and Lamprey River stations. DIN decreased at the Oyster River and Upper Piscataqua stations while Chapman’s Landing indicates an increasing trend.
  • Phytoplankton
    Based on monthly sampling at low tide, four of the eight stations periodically—though infrequently—exhibit high (>20 ug/L) levels for chlorophyll-a. There are no statistically significant trends.
  • Seaweeds
    At limited intertidal sampling sites, green and red seaweeds increased from 8% percent cover to 19% between 1980 and 2016. Two new invasive species are now the dominant red seaweeds.
  • Dissolved Oxygen
    In 2015, at the Great Bay and Coastal Marine Laboratory datasondes, dissolved oxygen levels never fell below 6 mg/L. Low dissolved oxygen events occur in all the tidal rivers. There are no clear trends.
  • Eelgrass
    Eelgrass acreage in the Great Bay is 31% less than when first mapped in 1981.
  • Salt Marsh
    Between the early 1900s and 2010, over a thousand acres of salt marsh area was lost in the Piscataqua Region watershed. As of 2017, approximately 5,521 acres of salt marsh habitat remain.
  • Bacteria
    Between 1989 and 2016, dry weather concentrations of bacterial indicators of fecal pollution in the Great Bay Estuary have typically fallen 67% to 93% due to pollution control efforts in most, but not all areas.
  • Shellfish Harvest Opportunities
    The percentage of possible acre-days between 2012 and 2016 was 80% and 66% for the Great Bay and Hampton-Seabrook estuaries, respectively, continuing the long-term trend of gradual increase in acre-days.
  • Beach Advisories
    Across the 17 tidal beaches in the Piscataqua Region watershed, beach advisory days occurred less than 1% of beach-days from 2012 to 2016. There are no statistically significant trends.
  • Toxic Contaminants
    Most concentrations of measured metals and organic chemicals in blue mussel tissue from 1991-2016 are declining or not changing. Mercury and PCB levels remain high enough to merit continued concern. Many emerging contaminants are not yet monitored consistently.
  • Oysters
    The number of adult oysters decreased from over 25 million in 1993 to 1.2 million in 2000. Since 2012, the population has averaged 2.1 million oysters, which is 28% of the PREP goal.
  • Clams
    The clam population in 2015 was 1.4 million and the percentage of clams infected by disease has significantly increased.
  • Migratory Fish
    Migratory river herring returns to the Great Bay Estuary increased 69% between 2012 and 2016; however, river herring returns have sharply declined for the Oyster and Taylor Rivers. No statistically significant trends.


Response indicators track some key actions we are taking to restore our estuaries.

  • Conservation Lands (General)
    As of May 2017, 130,302 acres have been conserved (15.5% of the total land area) representing an increase of 5% in new land area coming under conservation (41,555 acres) since 2011.
  • Conservation Lands (Focus)
    In 2017, 34.4% of Conservation Focus Areas (CFAs) in New Hampshire and 14.2% of CFAs in Maine were conserved, for a combined impact of 40.9% of progress toward the PREP goal.
  • Oyster Restoration
    More than 26 acres of oyster restoration efforts have taken place since 2011. For recent efforts, the actual area covered by oyster shell has decreased by an average of 63%, while one site increased by 30%.
  • Migratory Fish Restoration
    In 2016, 42% of the historical distribution for river herring in the Piscataqua Region has been restored. Additionally, removal of the Great Dam in Exeter in July 2016 has improved/enhanced river herring passage on the Exeter River.


Social indicators measure the social landscape that could impact environmental indicators.

  • Housing Permit Approvals
    There were a total of 19,483 multi-family and single-family permits issued between 2000-2015 for the 42 New Hampshire watershed towns. There were 331 permits issued for the 10 Maine watershed towns in 2015.
  • Stormwater Management Effort
    As of July 2017, of the 42 NH watershed towns - 8 have adopted the complete set of standards, 7 are in the process of adoption, 5 have partial or diffrent, and 22 have not adopted. The 10 ME towns adhere to a state-level standard.
  • Stewardship Behavior
    In 2016, there were 38,878 volunteer hours logged in the watershed through the work of six selected New Hampshire-based groups. In 2016, there were 524 people who signed up for 96 events through the Stewardship Network New England.