How does a canal lock work?

Find out how locks work, when they were first used, and the different types used on canals over the last few centuries.

What are canal locks for?

Canal locks change the water level in the canal so boats can go up and down hills. A lock is a stretch of canal that is blocked off at each end by solid gates. These gates are opened or closed to allow water to fill or drain from the lock.

When a boat enters a lock, the gates close behind it. You then wind the paddles open and water then fills or empties from the lock through small openings known as ‘sluice gates’. When the water in the lock reaches the same level as the next part of the canal, the lock gates in front of the boat are opened, and the boat passes out of the lock.

Read the transcript for this film
Engineers built locks as a way to move boats up or down hills.
This is our model to show how a lock works.
1. The boat moves into the lock
2. The lock gates close and the chamber fills with water
3. Once the water is level, the lock gates can open and the boat can move out of the lock

When were canal locks invented?

Locks have been used on canals since ancient civilisation. But it wasn’t until the 1770s that the large-scale construction of lock canals became widespread. By using locks, canals could follow a more direct route between destinations, making journeys quicker and allowing boats to travel through areas that once were inaccessible.

The first lock with gates at both ends was built in Holland in 1373. Each end of the lock had one gate that moved up and down, and were called guillotine locks.

In the 15th century Leonardo da Vinci invented the double mitre lock, which is still used today. The double mitre lock uses the force of the water to keep them tightly shut.

In the mid-18th century, engineer James Brindley introduced the idea of using locks on canals in the UK. 

Aerial view of double locks in Camden with a busy pub on the bank

Different types of locks

Locks come in many varieties but our handy guide can help you tell them apart

How often are lock gates replaced? 

Lock gates are made from wood and are immersed in water all year round, therefore they regularly need replacing.  On average, a lock gate will last for around 25 years. Each year we replace around 100 lock leaves. Each lock gate is unique and is made by hand using the same techniques as used 250 years ago. 

With 1,589 locks in England and Wales, crafting these gates is a year-round job for our specialist carpenters and joiners. 