Gravity currents are important phenomena that play a critical role in the advection of fluids in natural and man made environments. Boat locks, which are a common feature on many coastal waterways, are one type of system that can generate gravity currents. These locks usually have a set of vertically hinged gates at each end which, when opened, permit water from within the lock to exchange with the outside water in the form of gravity currents. By using the results from a series of laboratory experiments the properties of these gravity currents were examined when the lock water was heavier than the outside water. It was found that the swinging action of a lock gate had a significant influence on the rate at which the water initially leaves the lock as a slumping gravity current, with the initial speed of the flow being dependent upon the gate's opening speed. However, the final velocity achieved by the gravity current was independent of the gate opening speed; indicating that the total amount of entrainment of water into the flow was independent of opening speed.