Control lock

A control lock differs from a normal canal lock in that its primary purpose is controlling variances in water level rather than raising or lowering vessels.

For instance, Lock 8 is a guard lock near the south end of the Welland Canal at Port Colborne, Ontario, Canada. Due to the large expanse of shallow water in Lake Erie, changes in wind direction and force create water level changes as great as 11 feet at Port Colborne. Lock 8 controls the water level in the canal, keeping it independent of the fluctuations of Lake Erie, but still allowing ships to enter Lake Erie regardless of its level.