Sycamore Island is a 14-acre alluvial island in the Allegheny River at Blawnox, Pennsylvania, notable for remaining undeveloped and preserving rare natural features. Once considered the last privately owned undeveloped island in Allegheny County, it contains a floodplain hardwood forest, a plant community regarded as among the rarest in the world. Its ecological importance earned inclusion in the Allegheny River Biological Diversity Area, ranked of High Significance by the Allegheny County Natural Heritage Inventory. On December 28, 2007, Allegheny Land Trust acquired the island with Colcom Foundation funding, securing its permanent protection for ecological, educational, and recreational benefits.