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Aerial photograph from Great Bay National Estuary Reserve looking northeast

Zostera – (Eel Grass) bed along nearshore in autumn
Photograph from U.S. Fish and Wildlife Service

Bathymetry of Great Bay.  Depth in feet.  Only the central axis (light blue on chart) is navigable.
Chart from Navionics

Location                43o04'11.1" N     70o53’16.7"W


Trophic level oligotrophic (low phytoplankton with excess nitrogen from sewage discharge, with extensive areas of Zostera marina [Eel Grass]), maximum depth 17.7 m, average depth 2.7 m. area 23.1 km2.  Rapid tidal flushing prevents accretion of cyanobacteria and phycoplankton.

Great Bay Estuary is a drowned river valley composed of high-energy tidal waters, deep channels and fringing mudflats.  Most of the bay is too shallow for boat navigation except by small boats with minimal draft.  More than half the area of the bay is exposed as mud flats during low tide.  The entire water volume of the bay is replaced by an estimated average of nine tidal cycles.

Great Bay was formed ~14,000 years ago as the most recent Wisconsin-age glacier receded northward exposing the coast to rising sealevel.  Currently the major biological habitats in order of area include Zostera meadows, mudflats, salt marsh dominated by Spartina patens (Salt-meadow cordgrass in ‘high’ salt marshes) and Spartina alterniflora (Smooth cordgrass in ‘low’ salt marshes), channel bottom and rocky intertidal with red and green macroalgae.

Not a lake, Great Bay is an inland estuary located on the SE coast of New Hampshire receiving water from five tributaries including the Bellamy, Exeter, Lamprey, Squamscott and Winnicut.  It receives tidal water from the Piscataqua River and Little Bay.

In turn, the Piscataqua River receives inland water from two tributaries, the Cocheco and Salmon Falls rivers.  The mouth of the Piscataqua is Portsmouth Harbor that houses the submarine drydock called Portsmouth Naval Base.


Dates sampled


August 15, 2016


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