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Biomes and Ecosystems

Great Bay Estuary

by Brian W. Teasdale

Category: Marine and Oceanic Biomes.

Geographic Location: North America.

Summary: Advocates of this strongly tidal estuary, one of the most important such water bodies in the northeastern United States, have rallied around its Wildlife Refuges and Research Reserve to restore the imperiled habitats here.

Often considered New Hampshire's hidden coastline, the Great Bay Estuary is a complex embayment and one of the nation's most recessed estuaries. This waterway, situated just south of Maine's border, offers a variety of habitats that sustain a large biodiversity of wildlife. Current eutrophication, pollution, and habitat fragmentation due to human development are causing significant changes to the estuary.

Geography and Climate

This estuary is comprised of two large inland bays—Great Bay and Little Bay—and the Piscataqua River. These three bodies of water lie at the confluence of freshwater from seven major river systems, and the tidal seawater from the Gulf of Maine. Before reaching Great Bay, this seawater travels 15 miles (24 kilometers) inland through the Piscataqua River and Little Bay. The Piscataqua forms the northern end of the Great Bay estuarine system; it is directly controlled on its east side by oceanic tides, and along the northwestern edge by its inland tributaries, the Salmon Falls and Cocheco Rivers.

The more centralized Little Bay extends from the Piscataqua River southward toward Big Bay. Characterized by its many mudflats, the deep-channeled Little Bay is fed by the Oyster and Bellamy Rivers.

The final component, Great Bay, begins at Furber Strait, at which point seawater has already traveled inland through the Piscataqua River and Little Bay. In addition to tidal waters from the ocean, Great Bay is directly influenced by the continual input of freshwater from the Squamscott, Lamprey, and Winnicut Rivers.

The saltwater tidal exchange in the Great Bay Estuary has a significant effect on the bay's ecosystem. Despite freshwater continuously flowing from its tributaries, the estuary remains an ocean-dominated ecosystem. It takes close to 18 days during peak river flow for water to flush from one end of the estuary to the other. The tidal dynamics of this estuary, especially within the Piscataqua River, create some of the strongest currents in North America. The change in tides also produces a prominent change in the landscape, with the ebbing tide leaving more than half of Great Bay exposed as mudflats.

Temperature ranges in the summer (July) have average highs in the mid-70 to low-80 degrees F (24 to 28 degrees C), and average lows in the mid-50 to low-60 degrees F (13 to 15 degrees C). Temperatures in the winter (January) have an average high of 34 degrees F (1 degree C), and an average low of 0 degrees F (minus 18 degrees C). Precipitation in the area is roughly 40 inches (102 centimeters) annually.

Biodiversity

The entire Great Bay estuarine system provides a variety of habitats including eelgrass beds, mudflats, salt marsh, rocky intertidal, channel bottom, tidal creek, and upland forest and fields.

Horseshoe crabs are among the marine species that inhabit the Great Bay Estuary's many saltwater-dominated habitats.

GreatBayEstuary.jpg

(Thinkstock)

Because the bay is part of the North Atlantic Flyway, numerous species of waterfowl, shorebirds, and wading birds use it for migration and overwintering, including a large winter population of federally protected bald eagles. The bay area serves as New Hampshire's primary wintering area for black ducks. Many state-protected species use the refuge as well, including the common loon, pied-billed grebe, osprey, common tern, northern harrier, and upland sandpiper.

Commonly found fish species here include both saltwater and freshwater varieties. Striped bass (Morone saxatilis) have become one of the greatest success stories for marine fisheries in New Hampshire and Maine coastal waters. Also found along the coast are bluefish, flounder, mackerel, pollock, haddock, and Atlantic cod. The Piscataqua River is a migratory highway for herring and shad; further into the estuary, in more brackish waters, can be found more herring, striped bass, and occasionally an Atlantic salmon or lamprey. Horseshoe crabs, oysters, mussels, and clams also reside in the estuary, most notably oysters.

Human Impact

Historically, the Great Bay Estuary has been an important location for natural resources. Native American tribes including the Abenaki Nation and others inhabited the region for more than 11,000 years before the first European settlements began in the 1600s. They survived on the abundant fish, shellfish, waterfowl, and mammals that lived in and around the estuary. As the population of new, white settlers around the bay increased, new industries developed, including textiles, timbering, and agriculture. The water was used to support new industries and to move cargo further inland.

Over time, ecological changes have occurred in the bay due to increased human activity, including increased sedimentation, agricultural runoff, industrial waste, raw sewage, and other pollutants. In 1989, the Great Bay Estuary was formalized as a Great Bay National Estuarine Research Reserve by the National Oceanic and Atmospheric Administration (NOAA) and the National Ocean Service. In addition, the New Hampshire Fish and Game Department has designated Adams Point, a small parcel of land bordering the western shoreline of Great Bay, a Wildlife Management Area.

The University of New Hampshire's Jackson Estuarine Laboratory is located directly on the shoreline of Adams Point, allowing the university to specialize in Great Bay ecology through numerous ongoing research projects, including short- and long-term monitoring of the bay. Active areas of research at the laboratory include the ecology of estuarine seaweeds, nutrient cycling, fish populations, and shellfish aquaculture.

In 2009, a federally funded conservation unit, the Piscataqua Region Estuaries Partnership, generated a State of the Estuaries report on the health of Great Bay. The report warned that sprawling growth was having a negative effect on the bay, and that indicators such as increased nitrogen loading and poor dissolved oxygen concentrations were affecting water quality and threatening important submerged aquatic vegetation such as eelgrass (Zostera marina), a seagrass species vital for fish survival and sediment binding. As with many estuarine systems affected by human development in the last century, nonpoint pollution sources such as septic systems and fertilizers have been linked to the increased nitrogen loading in Great Bay.

Also of major concern are the impacts of climate change, which are already being studied in the estuary. These changes have substantial implications for the Great Bay ecosystem. New Hampshire and Maine are likely to experience warmer temperatures and increased flooding from storm events and a rising sea level. Species and habitats may shift in response to changes in these anticipated temperature and water levels.

Citation Types

MLA 9th

Teasdale, Brian W. "Great Bay Estuary." Biomes and Ecosystems, edited by Robert Warren Howarth, Salem Press, 2013. Salem Online, online.salempress.com/articleDetails.do?articleName=BIOMESECO_101536901239.

APA 7th

Teasdale, B. W. (2013). Great Bay Estuary. In R. W. Howarth (Ed.), Biomes and Ecosystems. Salem Press. online.salempress.com.

CMOS 17th

Teasdale, Brian W. "Great Bay Estuary." Edited by Robert Warren Howarth. Biomes and Ecosystems. Hackensack: Salem Press, 2013. Accessed September 24, 2026. online.salempress.com.

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