The Lamprey River is a 50.2-mile-long (80.8 km) river in southeastern New Hampshire, the United States. It rises in Meadow Lake in Northwood, and flows south, then generally east through Raymond, Epping, Lee, Durham and finally Newmarket. Here, it meets Great Bay, a tidal inlet of the Atlantic Ocean, to which it is connected by a tidal estuary, the Piscataqua River. The river from the Bunker Pond Dam in Epping to the confluence with the Piscassic River is part of the designated National Wild and Scenic River System.
The shoreline of the Lamprey River, its floodplain and its wetlands provide a wide range of valuable wildlife habitats. Its anadromous fishery is one of the strongest in the Great Bay watershed. Anadromous fish species that use the Lamprey River include shad, river herring, smelt and even Atlantic salmon. These fish are hatched in the river, then spend most of their lives out at sea, returning to the river to spawn. The fish species will move up the river as far as Durham, where they are prevented from moving further upstream by Wiswall Dam.
The river is also rich in species of freshwater mussels. The river is managed by the New Hampshire Fish and Game Department for several different types of game fish, including brook trout which is native to the river. Rainbow trout and brown trout are also stocked in many parts of the river but are not native to the area.
Lampreys are also present in the river. However, the Lamprey River derives its name from an early settler, John Lamprey, who lived in the area, rather than the fish itself.
Segments of the river are rich in history. Saw- and gristmills which operated by water power were common along the river. The Wiswall Falls Mills Site in Durham is on the National Register of Historic Places. Originally a sawmill, the site was used subsequently to make knives, nuts and bolts, pitchforks, carriages, matches and wallpaper. Sites such as Wadleigh Falls show the remnants of old mills and the rich river culture that used to be. Wadleigh Falls, located in Lee, is the remains of a dam created to power a mill which fed a 150-acre (61 ha) mill pond at one point.