About Our Estuaries

Estuaries are truly special places. They are partially enclosed bodies of water along the coast where the salt water of the ocean meets and mixes with the fresh water of rivers and streams. Estuaries and the lands surrounding them are places of transition – from land to sea and freshwater to salt water. Estuaries are among the most productive on earth, creating more organic matter each year than comparably-sized areas of forest, grassland, or agricultural land. The tidal, sheltered waters of estuaries also support unique communities of plants and animals especially adapted for life at the margin of the sea.

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Our Estuaries Facts:

  • Great Bay and Hampton-Seabrook Harbor, have approximately 220 miles of estuarine shoreline between Maine and New Hampshire
  • Approximately 337,350 people live in the 52 towns that make up the Great Bay and Hampton-Seabrook estuaries
  • There are 7 major rivers that flow into Great Bay estuary
    • Winnicut River
    • Exeter/Squamscott River
    • Lamprey River
    • Oyster River
    • Bellamy River
    • Cocheco River
    • Salmon Falls River
    • Great Works River
  • There are six rivers that flow into Hampton-Seabrook Harbor
    • Taylor River
    • Hampton Falls River
    • Browns River
    • Cains Brook/Mill Creek
    • Hunts Island Creek
    • Blackwater River
  • Great Bay itself covers an area of approximately 10,900 acres, or 17 square miles.
  • Great Bay estuary covers 1,023 square miles; 776 square miles are located within New Hampshire and 247 square miles are located in Maine
  • Great Bay has a 144-mile shoreline made up of steep wooded banks with rock outcroppings, cobble and shale beaches, and fringing saltmarsh.
  • 60% of the Great Bay watershed is covered by forests
  • Great Bay is one of the nation’s most recessed estuaries – seawater from the Gulf of Maine travels 15 miles inland through the Piscataqua River and Little Bay before flowing into Great Bay
  • Slack tides in the Squamscott River can be as much as 2.5 hours later than at mouth of Portsmouth Harbor
  • It can take up to 36 tidal cycles, or 18 days, to flush water through the estuary
  • There are 169 bird, fish and plant species that use the Great Bay Estuary in different ways at different times, 23 of these species are threatened or endangered at the state or federal level
  • Human history of the Great Bay region extends back over 11,000 when Native American tribes lived as hunter-gatherers on the natural treasures found in the estuary
  • 5 million metric tons of cargo is moved through the Port of Portsmouth Harbor each year
  • Hampton-Seabrook Harbor is a smaller bar-built estuary situated behind barrier beaches and surrounded by over 5,000 acres of saltmarsh.
  • Hampton-Seabrook estuary has an area of approximately 475 acres at high tide
  • Hampton-Seabrook estuary has approximately 72 miles of tidal shoreline.
  • Hampton-Seabrook estuary has the last remaining sand dunes in coastal New Hampshire
  • Hampton-Seabrook Harbor has the most productive clam flats in the state

PREP is part of the U.S. Environmental Protection Agency’s National Estuary Program, a joint program between local, state and federal agencies established under the Clean Water Act with the goal of protecting and enhancing nationally significant estuarine resources. PREP is supported in part by an EPA matching grant and is housed within the School of Marine Science and Ocean Engineering at the University of New Hampshire.