Holtwood Dam

In October 1905 McCall’s Ferry Power Co. began construction in Martic Township, Lancaster County, on what would be the second of four hydroelectric dams built to harness the power of the Susquehanna River below Harrisburg, Dauphin County. Twenty miles from the tidewater of the Chesapeake Bay, it was then the third longest dam in the world, built of solid concrete, 55 feet high. The project stalled as a result of the 1907 U.S. financial crisis, which necessitated the company’s reorganization. Financed by Canadians Herbert Holt and Edgar Wood, the Pennsylvania Water & Power Co. (PWP) was incorporated and began service in 1910, providing electricity to Lancaster and Baltimore. The facility was later named Holtwood after the two executives.

In 1912 the installation of the world’s first Kingsbury thrust bearing at Holtwood revolutionized the industry. The same thrust bearing remains in operation today and was designated as a Historic Mechanical Engineering Landmark by the American Society of Mechanical Engineers in 1987.

Impounded water from the dam creates the eight-mile-long Lake Aldred, now a popular boating destination, named for PWP president and chairman of the board John E. Aldred. Beginning around 1898 amateur archaeologist and Lancaster County native David Herr Landis anticipated the inundation and photographed imperiled Susquehannock Indian petroglyphs, or rock carvings, in the area. Later generations of notable archaeologists, including Donald Cadzow, Barry Kent, Paul Nevin and Kurt Carr, have more extensively documented the area, which is known to contain the highest concentration of petroglyphs in the northeastern United States. The backwater also trapped anthracite coal fines, which beginning in 1925 were used in an onsite coal-fired steam plant, making Holtwood the first facility to simultaneously operate a fossil-fuel and hydroelectric plant.

A century earlier, canal dams along the Susquehanna revealed that such barriers impeded migration of anadromous fish, particularly American shad. This prompted legislation in 1866 that led to the creation of the Pennsylvania Fish Commission (now Fish and Boat Commission). Despite Holtwood’s two original fishways, by 1911 national news  reports documented thousands of eels and pools of fish unable to navigate the ladders. Several studies and evolutions of fish passages have been incorporated since, including a $21 million installation of elevator lifts in 1997. Most recently a $434 million expansion that more than doubled the electrical output of the facility also addressed migration by modifying the fish lift, rerouting the discharge of Unit 1 and installing a downstream barrier dam preventing fish from entering the spillway. The project was completed in November 2014, nearly a decade after planning began.

Prior to plant modifications, natural big-water waves below the dam had become a popular attraction for the whitewater paddling community. Mitigating the effects of construction, the $4 million Holtwood Whitewater Park opened in March 2015.

Ownership of Holtwood was assumed by Pennsylvania Power & Light (now PPL) in 1955, when it merged with PWP. PPL has managed more than 5,000 acres in the vicinity as the Holtwood Environmental Preserve. Recently several of these tracts, including the Shenks Ferry Wildflower Preserve, Pinnacle Overlook and Kelly’s Run Natural Preserve, comprising a significant portion of the scenic Susquehanna Riverlands greenway corridor, have been conveyed to the Lancaster County Conservancy and the Pennsylvania Department of Conservation and Natural Resources. Holtwood Hydroelectric Plant was divested to Talen Energy, formed on June 1, 2015, through a merger with PPL and Riverstone Holdings LLC.

Josh Stahlman has been an archivist at the Pennsylvania State Archives since 2008.