Conewago Falls was a major natural barrier on the lower Susquehanna River in Lancaster County, Pennsylvania, near Three Mile Island and south of Harrisburg. At this unusually wide reach, the river dropped sharply along both sides of the island, making navigation difficult before the river was altered. Native Americans on the Susquehanna, including later Iroquois and Lenape travelers, portaged around the falls while moving between upriver Susquehannock towns and Chesapeake Bay. The falls also hindered barge and ship movement between Baltimore, the Chesapeake, and the Susquehanna interior. Much of the west side was later submerged by the York Haven Dam, completed in 1904, and now lies within Frederic Lake reservoir.