A flight of canal locks climbing a green hillside, with white-tipped black balance beams on each set of gates and still water in the pounds
AI-generated image, not a photograph of a real person or place.
theucl

AN INFORMATIONAL GUIDE: UNDERSTANDING CANAL LOCKS

A staircase
made of water.

FILL, THEN open the gates

  • Gates point upstream
  • Paddles move the water
  • Never both ends at once
  • Simple parts, clever result

A lock is a chamber with gates at each end.

Here UCL stands for understanding canal locks: this is an independent informational guide, not an organisation. Fill the chamber and a boat rises to the next stretch of canal; empty it and the boat sinks gently down.

Updated

Spot the lock

THE SHORT ANSWER

How a canal lock
lifts a boat.

The Canal & River Trust describes a lock
as a huge bath with taps and a plughole.

THE CHAMBER

Fill or empty

Opening the top paddles lets water in to raise a boat; the bottom paddles let it out to lower one. Boaters wind them with a windlass.

Spot the lock

THE GATES

Pointing upstream

Mitre gates meet at an angle of about 18 degrees, pointing upstream so the weight of the water keeps them shut.

See the numbers

THE CRANK

Wind the paddles

Paddles control the sluices. The Trust's tip: do not run the taps with the plughole open, or you waste water without filling the lock.

Lockside safety

SPOT THE LOCK

Which kind
is this?

Pick a lock type. The bar shows how likely you are to come across one on a canal walk, going by the Canal & River Trust's descriptions.

Lock spotter

Choose a type
A single pound lockEverywhere

Pound locks reached Europe in the 14th century and are the ones you see up and down the network. A single lock is the simplest and most water-efficient.

Locks stacked like stairsOn steep hills

In a staircase there are no pounds between chambers: the top gate of one lock is the bottom gate of the next. Foxton has two five-chamber staircases.

A shallow stop lockMostly gone

Built to stop one canal company taking another's water. With most canals now managed together, most stop locks have been removed.

A gate that lifts straight upA handful left

Guillotine gates rise vertically and need less space. Only a handful remain on canals; King's Norton's is a scheduled ancient monument.

Source: Canal & River Trust, Different types of locks; Boating through locks.

Based on the Canal & River Trust guide to different types of locks (April 2025). Availability varies by waterway.

TWO NUMBERS WORTH KNOWING

Caen Hill Locks
in numbers.

Both figures describe Caen Hill on the
Kennet and Avon Canal, near Devizes.

≈ 123,000 litres

Water used by each Caen Hill lock, every time

Each lock fills and empties over 2,000 times a year. Water is pumped from the Bristol Avon at Claverton, 13 miles away, and around each flight.

WATER · CANAL & RIVER TRUST

237 feet

Rise of the 29-lock flight

Over two miles, a gradient of 1 in 44. The steepest 16 locks are a scheduled ancient monument, and the flight takes five to six hours by boat.

CLIMB · CANAL & RIVER TRUST

The Canal & River Trust says sharing locks with other boats helps keep water in the waterways.

FIVE SAFETY HABITS

Lockside safety:
edges and water.

Water churning white as it pours into a stone lock chamber through opened paddles
AI-generated image, not a photograph of a real person or place.

From the Canal & River Trust's boaters' handbook and water safety advice.

  1. Mind the edges

    Watch out for unprotected drops around the lockside, especially when gates are being opened.

  2. Expect slippery ground

    Lockside surfaces and gate beams can be slippery when you push the gates.

  3. Wait your turn

    Wait for a boat in the lock to leave before touching the paddles, and ask before helping other boaters.

  4. Stay out of the water

    Cold shock, hidden objects, unexpected depths and untreated water make canals no place for a swim.

  5. Take care after a drink

    The Canal & River Trust asks people to take extra care next to water after a few drinks, and to choose a route home away from the water.

A LONG HISTORY

A short history
of canal locks.

A hand turning a steel windlass on the paddle gear beside a canal lock gate
AI-generated image, not a photograph of a real person or place.

The Canal & River Trust dates the introduction of locks to the 10th century and the arrival of pound locks in Europe to the 14th century. Steep flights sometimes use side ponds to top up each lock after use.

Broad locks are double the width of narrow ones, taking two narrowboats together or one wide boat, while double locks were built side by side so more boats could pass at once.

Questions

Questions people ask

What does UCL stand for on this site?

Understanding canal locks. This is an independent informational guide, not an organisation, club or company.

How does a lock raise a boat?

The boat enters the chamber, the gates behind it close and the top paddles let water in until the level matches the canal above. Then the top gates open.

Why are lock gates angled?

Mitre gates meet at roughly 18 degrees pointing upstream, so the weight of the water presses them shut, according to the River Wey Trust.

What is the difference between a flight and a staircase?

A flight has pounds of water between its locks. A staircase has none: each chamber's top gate is the next chamber's bottom gate.

Can I help boaters with the gates?

Ask first. The Canal & River Trust advises waiting for a boat in the lock to leave before operating paddles, and asking before helping.

How should a boat crew work a lock safely?

The Canal & River Trust's Boaters' Handbook advises taking your time, entering and leaving slowly, and always having a competent person on board while the boat is in the lock. Keep the boat well away from the gates and cills, as boats bang about when water flows in and out, make sure fenders cannot catch on the lockside or gates, and agree clear signals between crew and skipper, such as one that means close all the paddles.

How long does it take to boat through Caen Hill?

Typically five to six hours. The Canal & River Trust asks boaters planning to go up or down the flight to talk to its volunteer lock keepers, who have the experience to make sure water is conserved during the passage. Visitors can meet the volunteers at The Admiral, the welcome boat by Lock 44.

Sources

Where the facts come from

  1. Canal & River Trust: Boating through locks (Boaters' Handbook)
  2. Canal & River Trust: Different types of locks
  3. Canal & River Trust: Caen Hill Locks
  4. Canal & River Trust: Safety on our waterways
  5. River Wey Trust: How locks work

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