 The varied terrain created many interface zones biologically nurturing a great many species and many of those habitats effectively created difficult walking and horseback terrains which stifled east-west crossing of the lower Susquehanna in colonial Pennsylvania-Maryland spurring the 1730 opening of the historic Wright's Ferry and (later the first two) Columbia-Wrightsville Bridges, once believed to be the longest covered bridges in the world.The dam is located just above the confluence of the Conestoga River with the Susquehanna, about 7 miles downstream of Washington Boro, Pennsylvania, which at mid-river is figured more or less the center of Lake Clarke The Safe Harbor Water Power Corporation operates the dam and power plant.Planning for the construction of the Safe Harbor dam started in 1929 and construction started 1 April 1930.