John Paul Hammerschmidt Lake is a reservoir on the Arkansas River and an integral part of the McClellan–Kerr Arkansas River Navigation System (MKARNS). It was formed by constructing the 13 across the river, near the city of Barling, Arkansas and extends upriver 26 miles (42 km) to W. D. Mayo Lock and Dam, which is located inside the state of Oklahoma. Although the Trimble facility was completed in 1969, it was not allowed to pass commercial barges until 1971, when upstream facilities were completed. The normal elevation of the lake is 392 feet (119 m) above sea level.