The Marked Tree Lock and Siphons are a flood control facility on the St. Francis River in Poinsett County, Arkansas. These facilities are located about 9 miles (14 km) north of Marked Tree. Built in 1926, the lock is located on a now disused and partially filled artificial channel west of the main river. It has a concrete trough about 130 feet (40 m) long and 30 feet (9.1 m) high, with a small brick control house from which four gates are operated to regulate water flow through the lock.