The advancing and retreating mile-high glacial sheet of ice and snow shaped the countryside around Pymatuning, and as the last ice masses melted a great swamp developed, marked by towering white pines, bogs, and wetlands fed by the Shenango and Beaver Rivers. Abundant wildlife drew prehistoric and later historic Native Americans into the area, where they lived and hunted for thousands of years. Indian legend says that the name Pymatunging means "The crooked-Mouthed Man's Dwelling Place," referring to a Native American chief who once lived there. In the 1700s European trappers entered these swamp lands in search of beaver and other fur-bearing animals. After 1800 pioneer farmers and lumbermen came, but settlement in the swamp was slow and difficult, and eventually much of the area was cultivated in onion and other root crops. Change came in 1913 when the Pennsylvania Legislature passed the Pymatuning Act, proposing a dam to regulate the flow of the Shenango and Beaver rivers in Pennsylvania and conserve water for industry, household use, flood control, and recreation. Construction of the dam began in 1931 and was completed in 1934, creating the Pymatuning Reservoir across lands in Ohio and Pennsylvania. The reservoir is 16.5 miles long and 3.5 miles wide, with 70 miles of shoreline, a maximum depth of 35 feet, and a storage capacity of 67.3 million gallons of water, and it has long supported recreation including camping, hunting, fishing, hiking, sightseeing, swimming, and winter sports, with both Ohio and Pennsylvania managing state parks along its shores.