Lock 21 was the western entrance to the Cornwall Canal which ran for 11 miles along the Canadian shore of the St Lawrence river and was built to bypass the Longue Sault Rapids. The initial canal was constructed around 1840 and could only handle ships with an eight foot draft and operated for approximately 50 years. The lock that remains today was upgraded around 1898 when the entire length of the canal was deepened to handle ships with a greater draft up to 14 ft. At that time the first hydro generating station was constructed to electrify the entire length of the canal. It’s also claimed that Thomas Edison was at the opening of the new generating station and canal. The entire site was inundated with the completion of the new seaway in 1958 and the tops of the walls are now in 35 feet of water with the floor of the lock at the 60 foot level. The weir contains small gates about 4×4 feet square, two of which are still open and accessible to divers who want to experience the force of the river by getting flushed through them. At one time, initiation required that a diver swim up current through these gates, not a small feat I can assure you from personal experience. The lock gates were removed as they floated and would pose a hazard to the new generators downstream but the old wooden floor in the lock remains along with much of the hardware and machinery that controlled the weir. The handrails are still intact and offer great handholds in the stiff currents around the tops of the walls over which the river now flows. Immediately in front or behind the walls there is just enough current to keep the silt away and a slight back eddy will return a diver to the weir/entry point after a “fly through” of the lock itself.