Allegheny Islands Wilderness is a protected area in northwestern Pennsylvania within Allegheny National Forest along the Allegheny River between Buckaloons Recreation Area and Tionesta. Established by Congress in 1984, it includes seven alluvial islands totaling 368 acres, among the smallest wilderness areas in the United States. Instead of mountain or extensive forest terrain, it preserves low river islands shaped by sediment deposits and covered with river-bottom forests. Crull's and Thompson's islands hold 156 acres of mature and old-growth forest. The wilderness is especially significant for its rich river habitat, supporting returning bald eagles, reintroduced otters, rare mussels, uncommon fishes, and other wildlife.