What is a lock?
Updated on: 26/05/2025In inland waterway navigation, a lock is a structure that acts as an elevator for boats, allowing them to move from one navigable section to another located at a different elevation. A lock consists of an upstream gate and a downstream gate, with a chamber between them that fills with water or empties depending on whether the boat entering it needs to be raised or lowered.
A lock can be:
- Manual: you operate it yourself.
- Automatic: a few dozen meters before the lock, you pull a lever to signal the waterway control center to open the lock.
- Operated by a lock keeper: in this case, a waterway official operates the lock.
The process of passing one or more boats through a lock is called "locking" (generally a maximum of 3 or 4, depending on the size of the lock chamber).
On a canal, the section between two locks is called a reach or stretch.
Note that lockage consumes water: in fact, every time a boat passes through, regardless of the direction, water is transferred from upstream to downstream, which tends to lower the water level in the upstream section. This is why, during droughts, navigation and lockage may be prohibited to conserve water.
