The building of the Shannon hydroelectric scheme in the late 1920s required navigation to be maintained down to Limerick after the Parteen Weir cut off the old route via O'Briensbridge. This was achieved by building a double staircase lock at the Ardnacrusha power station. Taken from the approach canal this shows the entrance to the lower lock which has a rise of 34ft whilst the top lock has a rise of 68ft. This is the deepest lock in Britain and Ireland.