Allegheny Islands State Park occupies three alluvial islands in the Allegheny River northeast of Pittsburgh and preserves a small, distinctive piece of the region’s river geography. Established on December 31, 1980, the roughly 50-acre park remains intentionally undeveloped, with no built facilities, access only by boat, and camping permitted. Its islands reflect both natural processes and human change: Twelve Mile Island is partly occupied by houses, while the other two islands were once a single Fourteen Mile Island before a nearby lock and dam divided them. Set among six alluvial islands near Pittsburgh, the park stands out for its sediment-shaped landscape rather than amenities.