The Oyster River is about 17 miles (27.5 km) long and located in Strafford County, southeastern part of the state. It rises in Barrington, flows southeast to Lee, then east-southeast in a serpentine course past Durham to meet the entrance of Great Bay into Little Bay. The bays are tidal inlets of the Atlantic Ocean, to which they are connected by a tidal estuary, the Piscataqua River.
The Oyster River reaches tidewater at the base of a dam in the center of Durham, just west of the river's crossing by NH Route 108. Due to siltation, the river is only fully accessible to motorized boats west of the Durham Water Plant for approximately 3 hours on either side of high tide.
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