Pymatuning State Park in northwestern Pennsylvania is the state’s largest park, centered on Pymatuning Lake, a broad shallow reservoir that reshaped a former swamp along the Pennsylvania-Ohio border. The area was first inhabited by Mound Builders, later by the Lenape, and then controlled by the Seneca until white settlement followed the Treaty of Greenville. After flood control plans advanced in the early 20th century, major work began in 1931 and the dam was completed in 1934, creating a lake known for recreation, wildlife, and fishing. With gamelands, natural areas, a fish hatchery, and the Linesville spillway, it remains one of Pennsylvania’s leading outdoor destinations.