Holtwood Environmental Preserve is a protected landscape in southeastern Pennsylvania spanning more than 5,000 acres near Holtwood Dam on the Susquehanna River, across parts of Lancaster and York Counties. It brings together river scenery, woodland habitat, historic places, and recreation within one preserve. Among its most significant natural features is a 200-acre mesophytic old-growth forest along the Otter Creek gorge, with eastern hemlock, chestnut oak, and umbrella magnolia. The preserve also provides nesting habitat for bald eagles and ospreys. Its broader landscape includes camping, boating, hiking, Shenks Ferry Wildlife Preserve, the Indian Steps Museum of Native American Artifacts, and the Lock 12 Historic Area.