The Pennsylvania Water & Power Company was incorporated in Pennsylvania on January 14, 1910 for the generation of hydroelectric power for commercial and manufacturing purposes. The company was the result of the reorganization of the McCall Ferry Power Company, which was formed in 1905 for the construction of a hydroelectric dam along the Susquehanna River about ten miles northwest of the boundary line between Pennsylvania and Maryland at the village of McCall Ferry. After completing about eighty percent of the dam, the McCall Ferry Power Co. fell into bankruptcy during the Panic of 1907. In 1909, the company was sold to John E. Aldred (May 15, 1864-November 21, 1945), then president of the Shawinigan Falls Power Company in Canada, who helped refinance the dam project with two Canadian bankers, Sir Herbert S. Holt (February 12, 1856-September 29, 1941), president of the Montreal Light, Heat & Power Company, and Edward R. Wood (May 11, 1866-June 16, 1941), a Toronto financier and industrialist. Upon its completion in 1910, Aldred renamed the dam and the surrounding village Holtwood in honor of the Canadian bankers’ last names. Aldred appointed Charles E. F. Clarke (October 13, 1863-August 25, 1933) president and treasurer of the company in 1915, while James L. Rintoul (May 2, 1882-November 25, 1951), who became executive vice president in 1944, took over as treasurer in 1917. At the time operations began, the Holtwood Dam was a half a mile in length, about fifty-five feet in height, and was the second longest dam in the world at the time. In 1912, the hydroelectric plant had the capability to produce about 120,000 H.P. of electrical current and served Baltimore and surrounding areas in Maryland. Several companies relied on electricity from Holtwood, including the Consolidated Gas, Electric Light and Power Company of Baltimore and the United Railways and Electric Company, also of Baltimore. Through an exclusive contract, Consolidated Gas, Electric Light and Power Company of Baltimore and its affiliates controlled all of Pennsylvania Water & Power Co.’s power generation in the city of Baltimore. Although its works were in Pennsylvania, Pennsylvania Water & Power was effectively a Baltimore company, and its headquarters were in that city. As a result, it was not embroiled in the political controversies affecting Pennsylvania utilities, particularly during the administrations of Progressive Gov. Gifford Pinchot.

In 1910, Aldred brought in John Abbet Walls (September 5, 1879-May 1964) as chief engineer of the Holtwood Dam. Walls was born in Lewisburg, Pa., attended Bucknell Academy from 1891-1894 and completed his civil and electrical engineering degree at the Massachusetts Institute of Technology in 1899. Before taking the position at Holtwood, Walls worked in the engineering office of Wallace C. Johnson in Niagara Falls, New York, and, under the supervision of Aldred, took on the chief engineer position at the Shawinigan Water & Power Co. from 1901-1909. Before being named president of Pennsylvania Water & Power Co. in 1933, Walls spearheaded numerous improvements at the Holtwood facility, and looked towards other examples of hydroelectric development both nationally and internationally during and after the First World War. Such examples included innovations at plants in Austin, Texas, Italy, and Germany. Company officials also looked to benefit from the consumption of their own electricity. In 1915, several Pennsylvania Water & Power Co. officers, including Walls and Clarke, organized the Shawinigan Electro Alloys Company, later renamed the Baltimore Electro Alloys Company. Using their own source of electricity in the city of Baltimore, the company operated electric furnaces to manufacture ferro-silicon and other electric furnace products.

Of particular importance to the hydroelectric and steam power industry was Pennsylvania Water & Power Co.’s construction of a steam station that used pulverized coal dredged from the Susquehanna River. Millions of tons of fine anthracite coal that had been piled as a waste product of the coal breakers washed down the river from Pennsylvania’s anthracite regions, causing fears that siltation would interrupt the river’s flow past the dam. As a result, Walls and other company officials formed the Holtwood Coal Company (November 24, 1920) and the Anthracite Production Corp. to dredge coal from the river. The utilization of this river coal proved difficult at first, as most steam generation units in the United States burned coal on a grate, while the solution at Holtwood would be to use pulverized anthracite coal blown into the boiler. Very few blower-type furnaces existed in the United States at the time, and Walls assigned engineers to study those in use at plants in Lykens, Pennsylvania, and Niles, Ohio. Walls approved the installation of this new type of blower furnace, and construction began in 1924. The plant burned the coal recovered from the river in an adjacent steam electric generating facility. The utilization of this fine river coal continued and the company expanded its steam generation capacity through the 1940s and 1950s. River coal was used until the 1970s when, as mining upriver declined, the supply quickly dwindled to the point where it became unprofitable to continue dredging the river.

With the growth in demand for electric power, Pennsylvania Water & Power sought to expand their operations. On February 19, 1929, Consolidated Gas, Electric Light & Power and the Pennsylvania Water & Power formed the Safe Harbor Water Power Corporation for the construction of a new hydroelectric facility at Safe Harbor, just eight miles upriver from Holtwood. Operations at the new $30 million Safe Harbor facility began in 1931, and largely served the Consolidated Company in Baltimore and, in 1934, the electrification of the Pennsylvania Railroad. As at Holtwood, engineers at the Safe Harbor plant initiated several innovations, including the use of Kaplan turbines, then the largest propeller-type water wheels ever built in the United States. Both the Holtwood and Safe Harbor plants served as models for larger dams later built by the United States government in the South and West.

The Safe Harbor facility marked the end of hydroelectric development along the Susquehanna River in Pennsylvania and Maryland. However, the September 16, 1927 formation of the Pennsylvania-New Jersey Interconnection, the world’s first fully integrated intercompany power grid, brought electricity to much of the Chesapeake and eastern Pennsylvania area, including to factories, businesses, houses, and farms. On June 1, 1955, Pennsylvania Power & Light Company (PP&L, later PPL Electric Utilities Corporation), which formed in 1920 by the merger of eight utilities companies serving eastern Pennsylvania, acquired Pennsylvania Water & Power, and became the owner of the Holtwood plant and part owners of the Safe Harbor plant. PP&L continued to operate the Holtwood plant until June 1, 2015, when, in response to the changes brought about by deregulation, PPL spun off the dams and all its power generating facilities to Talen Energy Corporation, now an independent power producer headquartered in Allentown, Pennsylvania.