Conewago Falls in Lancaster County, Pennsylvania, was a historic river barrier 12 miles (19 km) below and south of Harrisburg at a wide spot, where the river drops 19 feet (5.8 m) in 1⁄4 mile (0.40 km) along the lower Susquehanna River along either side of Three Mile Island. The falls between the west bank and the west side of the island were inundated-by-design years ago by construction of the York Haven Dam which, when it was completed in 1904, for a time became the third largest in the world. Today the Falls hides inside the Frederic Lake reservoir along the west side of the island.