Marsh Lock is a lock and weir situated on the River Thames in England, about 1 mile upstream of Henley Bridge in Henley-on-Thames, Oxfordshire. The lock is close to the Berkshire bank, but accessed from the Oxfordshire side via two long walkways, the downstream one being near Mill Meadows. The first pound lock was built by the Thames Navigation Commission in 1773. The weir consists of a series of iron watergates running from the lock to the Oxfordshire bank near the mills. It is situated between the two walkways.