Southern New England-NY Bight Coastal Program
Northeast Region

Fish Passage


Mill neck barrier

There are over 5,400 large dams in Massachusetts, Rhode Island, Connecticut, New York, and New Jersey as well as thousands of low head dams and water control structures that prevent fish migrations.  Many of these obstacles are within the boundaries of the SNEP program area and block important riverine habitat for several migratory fish species.  Removing barriers is critical for the survival of several species including alewife and blueback herring, American shad, sea-run brook trout and American eel.  In order to protect and restore habitat for fish, the office provides funding and technical expertise, and collaborates with U.S. Fish and Wildlife Service offices, other federal and state agencies, NGOs, private landowners and corporate interests.  Restoring rivers and increasing fish populations boosts the biological productivity of the entire river corridor, as well as estuaries and oceans for every living thing including aquatic insects, mussels, waterbirds, furbearing mammals, seabirds, marine mammals and commercially and recreationally important fish.

Dam removal is the best all around method for achieving fish passage because it removes a barrier and restores full function to a natural system. Even though dam removal would provide the best habitat for fish, often many dams need to be maintained because of their function: hydro power generation, water supply, flood control, or their historical or aesthetic significance. 



When building a fishway SNEP provides the biological expertise and partner building as well as access to our U.S. Fish & Wildlife Service Fisheries Division hydraulic engineers who are highly regarded fish passage experts in North America.  Working closely with our state fish biologist, we can provide a conceptual plan for a fishway; location, basic design, slope, and configuration.  This information can then be used by a professional engineer with experience in fishway design to develop plans suitable for construction. 


Building a fish ladder

Fish passage can be achieved in a number of ways which are usually constrained by the individual site characteristics.  Depending on the site, completely removing a dam is an option as well as partial breaching of the dam structure when appropriate. Other options are to provide engineered technical fishway or a nature like fishway.  Technical fishways employ engineering designs that are typically concrete or aluminum fish ladders in a style known as a Denil fishway design.  These structures provide a cascading effect which slows the water velocity and allows for design of specific swimming speed that the desired species can manage.   Other engineered devices called Nature-like Fishways are designed to mimic nature by providing a smaller bypass stream around a dam.  Lastly, rock ramps create a rock cascade covering the entire width of the channel and on a 1:30 slope makes a white-water ramp that goes up and over the existing dam.  This design is effective for passing diadromous as well as resident species and is constrained to low head dams.

View SNEP 2009 fish passage projects and accomplishments.

Last updated: July 18, 2012

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