The Killaloe Canal bypassed some of the rapids on the Shannon.
The canal had three locks, but the two downstream were submerged when the Ardnacrusha Hydro-Electric power station was built in the 1920s.
A lock is a lift for boats. A boat coming upstream enters the lock chamber, where the upper gates are already closed; the lower pair of gates is then closed behind it and water is let into the chamber until it is level with the water on the upstream side. The upper gates are then opened, and the boat leaves the lock. Killaloe Lock had provision for four pairs of gates; two pairs pointing to the lake and two pointing to the canal. This unusual arrangement would have allowed the lock to operate if the level of the lake fell below that of the canal.
The lock keeper worked the lock; his house stood where the library is now.
Killaloe-Ballina