The Wiswall Dam, located on the Lamprey River, has an 11-foot-high spillway and is 200 feet in length. It is a concrete gravity dam, built circa 1911 and is classified as a Class B, or significant hazard, dam. The Town of Durham purchased the dam to secure the impoundment as a back-up water supply. Recreational and aesthetic considerations are significant for residential property owners along the impoundment.

Annually, fish swim through the fish ladder at MaCallen Dam in Newmarket, NH, which is three miles downstream; however, Wiswall Dam impedes further upstream movement. The Lamprey River is the most significant river for anadromous fish in NH, and thus was designated as a National Wild and Scenic River in 1996.

During the Wild and Scenic River Designation process, the subject of dam removal was only briefly considered because the impoundment was seen as critical to the Town water system. However, recent analyses of the Town water system and its relationship to the river addressed the possibility that an adjacent aquifer might provide both their needs. If developed, this could potentially replace the water storage capacity lost through removal of the dam. The analyses also emphasized that dam removal would result in more complete restoration of the natural ecosystem. While a fish ladder would benefit certain species, dam removal would allow movement of a greater number and variety of fish species and other aquatic organisms up and down the river. Dam removal would also result in improved water quality. It was thus decided to expand the fish passage restoration study to include two options: installation of a fish ladder and complete removal of the dam. The USACOE study was expanded to an analysis of the comparative costs, benefits and impacts of the two options.

Since June 2001, project partners have met eight times and held a Public Information Meeting to discuss the project and the USACOE study of the two options. A preliminary study plan has been proposed, with additional components to be considered as brought to attention through agency input and public participation.

When a fish passage option is decided, fish will access up to 45 miles of additional riverine habitat in the mainstem and tributaries. This would allow about 20,000-60,000 alewives, blueback herring and other fish species (Atlantic salmon, American shad, American eel, brook trout, brown trout, rainbow trout, sea lamprey and smallmouth bass) continued upstream migrations.

National Park Service, Lamprey River Advisory Committee, Town of Durham, University of New Hampshire, Dufresne-Henry Inc. (the Town and University consultants), the U.S. Environmental Protection Agency, the U.S. Army Corps of Engineers, New Hampshire Department of Environmental Services, FishAmerica Foundation, Trout Unlimited, Coastal Conservation Association, and the Hackle and Tackle Club.