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Dams are a major threat to the recovery of Atlantic Salmon

Habitat loss from existing dams found on Maine's rivers and streams pose some of the greatest threats to the survival of listed Atlantic salmon.  Many small dams within the freshwater range of the GOM DPS of Atlantic salmon are not designed to safely and effectively provide passage for anadromous fish such as Atlantic salmon, alewives and American shad, in addition to resident freshwater species and other aquatic organisms.

Dams can impact listed Atlantic salmon in the following ways:

  • Dams can cause migratory delays for returning adults or outmigrating smolts. These delays may have detrimental effects on the physiology of a salmon; which in turn, affects survival and reproductive success.
  • Dams can impair or block access to quality spawning and nursery habitat and cause a loss of connectivity between important habitat types needed to sustain the species.
  • Dams may increase predation on Atlantic salmon by altering river habitat to lake-like conditions; many dams create habitat that is better suited for species such as bass and pickerel that are known predators of salmon.
  • Dams can impair water quality and impact aquatic habitat by altering flow dynamics of natural stream channels.
  • Dams are known to increase water temperatures and decrease dissolved oxygen levels. Atlantic salmon require cool, well oxygenated rivers to survive and reproduce.




Meadow Dam, Orrington, Maine.  Credit: NOAA


Currently, over 470 dams impair or block access to approximately 90 percent of freshwater habitat necessary to support Atlantic salmon spawning and rearing of juveniles.

For more information on the biology and status of the species, please visit the Atlantic Salmon Recovery Program.

Construction (left) of a fishway (above) on the Blackman Stream. 
Credit: Atlantic Salmon Federation