Migratory Fish Restoration

How many miles of main stem freshwater rivers are accessible to river herring in the Piscataqua Region?

As of 2016, 42% of the historical distribution for river herring in the rivers of the Piscataqua Region has been restored. Additionally, removal of the Great Dam in Exeter in July 2016 has improved/enhanced river herring passage on the Exeter River.


Physical barriers such as dams and culverts can prohibit the movement of migratory fish between upstream and downstream areas. Migratory fish–such as river herring–live mostly in saltwater, but travel upstream to freshwater to reproduce. Limiting passage to freshwater upstream can limit populations.
Restore native migratory (diadromous) fish access to 50% of their historical main stem river distribution range by 2020.
Coastal rivers of the Great Bay Estuary historically supported abundant fish returns for river herring (alewife and blueback herring) and American shad. However, during the 19th century the construction of dams along coastal rivers limited access to freshwater spawning habitats.53 To support recovery of river herring populations in the 1950s, NH Fish and Game began efforts to restore access to historically accessible freshwater streams and ponds. Figure 20.1 shows the historically accessible miles of freshwater in the main stem of each major river, and how many miles of freshwater habitat are currently accessible. For this indicator, fish ladders are considered to provide limited access for migratory fish, however, fish ladders on the Winnicut Dam in Greenland and former Great Dam in Exeter are inefficient at passing river herring to upstream spawning habitat.

For the Exeter, Cocheco, and Winnicut Rivers 100% of freshwater miles historically accessible are once again open for fish passage as of 2017, assuming fish ladders provide limited access. Less than 30% access is open for the remaining main stem rivers. Overall, freshwater access for river herring has been restored to 42% of historical distribution within the main stems of the region’s major rivers (Figure 20.2).

Figure 20.1 Mainstem stream miles accessible to river herring in major rivers of the Piscataqua Region. River miles historically accessible to river herring and total river miles open to river herring as of 2016.

Figure 20.2 Upstream river miles re-connected for migratory herring on the mainstems of major rivers.