Although New Hampshire has just over 18 miles of Atlantic coastline, the state's two major estuaries, Great Bay and Hampton-Seabrook Harbor, have approximately 220 miles of estuarine shoreline. The two estuaries differ in their geology, hydrology, and history, but both are valued for their beauty and rich array of natural resources, which, along with Rye Harbor and Little Harbor, provide numerous commercial and recreational opportunities for New Hampshire's citizens.Great Bay, the state's largest estuary, is a tidally dominated system encompassing an area of approximately 10,900 acres, or 17 square miles. Two-thirds of the estuary's 930 square mile watershed is located within New Hampshire. Eleven New Hampshire communities border Great Bay, which has a 144-mile shoreline made up of steep wooded banks with rock outcroppings, cobble and shale beaches, and fringing saltmarsh. The phase of the tide lags significantly as you move from the ocean up into the estuary, with slack tides as much as 2.5 hours later in the Squamscott River than at the mouth of Portsmouth Harbor. It can take up to 36 tidal cycles, or 18 days, to flush water through the estuary during periods of high river flows.
photo by Steve Mirick
Hampton-Seabrook Harbor is a smaller bar-built estuary situated behind barrier beaches and surrounded by over 5,000 acres of saltmarsh. Covering an area of approximately 475 acres at high tide, this estuary has approximately 72 miles of tidal shoreline. Sandy beaches, including some of the last remaining sand dunes in coastal New Hampshire, are a popular tourist attraction adjacent to and within the estuary. The Hampton-Seabrook Harbor also serves as a popular clamming destination and has the most productive flats in the state.
Photo by Mike Morrison