Each lock has room for several vessels at a time. Once they’re moored, the lock operator slowly fills or empties the lock.
To empty the lock – for vessels descending the Rhine – water runs out through the wickets in the tailbay gates. When the water attains the lower Rhine level, the lock gates open and the ship passes into the outer dock.

When vessels are ascending, the top section of the paddle gate in the forebay of the northern lock is briefly raised. Water flows into the lock chamber until the water level reaches the level of the outer dock on the upper reach. The top section of the paddle gate is then lowered to allow vessels to sail across.