Locks and weirs on the River Thames

The English River Thames is navigable from Lechlade to the sea, and this part of the river falls 71 metres (234 feet). There are 45 locks on the river, each with one or more adjacent weirs. These lock and weir combinations are used for controlling the flow of water down the river, most notably when there is a risk of flooding, and provide for navigation above the tideway.


From the Middle Ages, the fall on the river in its middle and upper sections was used to drive watermills for the production of flour and paper and various other purposes such as metal-beating. This involved the construction of weirs in order to divert water into the mills. The weirs, however, presented an obstacle to navigation and to solve this problem locks were built alongside the weirs to enable boats to be moved between levels.

Originally these were flash locks that were essentially removable sections of weir. A boat moving downstream would wait above the lock until the lock was opened, which would allow a "flash" of water to pass through, carrying the boat with it. In the opposite direction boats would be winched or towed through the open lock. The difficulty of using flash locks, and the consequent loss of water and income to the miller, eventually lead to their replacement with pound locks. Locks similar to these early pound locks still exist on the river, although in many cases they have been enlarged and mechanised.

On the lower section, the river was tidal as far as Staines until the beginning of the 19th century and was under the control of the City of London. The City's jurisdiction was marked by the London Stone. The principle of lock/weir combination, which maintained the depth of water for navigation and reduced the danger of flooding, was extended over the tidal section as far as Teddington in a series of locks built after 1810.

The first authority charged with managing navigation and lock building was the Oxford-Burcot Commission, which built the locks at Iffley and Sandford below Oxford in 1633. In 1751, the Thames Navigation Commissioners were established and built the locks from Days Lock to Boulters lock between 1770 and 1790. The locks built on the tidal section required individual Acts of Parliament, and the Thames Conservancy took over their management from the City in 1857. In 1866 the Thames Conservancy became responsible for all river management and installed more locks over the years, the last being Eynsham and King’s in 1928. The Thames Conservancy was subsumed into the Thames Water Authority in 1974. With the privatization of water supply in 1990 the river management functions passed to the new National Rivers Authority and in 1996 to the Environment Agency. Only Richmond Lock remains under the jurisdiction of the Port of London Authority.


From the head of the river to the start of the tidal section at Teddington Lock, the river is managed by the Environment Agency, which has the twin responsibilities of managing the flow of water to control flooding, and providing for navigation. As a result all the locks and weirs on the river, except the semi-tidal Richmond Lock, are owned and operated by the Environment Agency. Richmond Lock is managed by the Port of London Authority.

Each of the Environment Agency's locks and weirs is manned by a lock keeper, who normally lives in a house adjacent to the lock. The lock keeper's duties involve both operating the lock, and managing the river levels above the lock by adjusting the weir openings.


Most locks are operated by their keepers between 9 a.m. and 7 p.m. from June to August, with progressively shorter hours as the hours of daylight reduce, and they are not operated during the lock-keeper's lunch hour between 1 p.m. and 2 p.m. During the summer months Assistant Lock Keepers are employed to deal with the heavy traffic and avoid the lunch-time closure. However Teddington Lock, which is the most downstream of the Environment Agency locks and separates the non-tidal river from the tideway, is manned 24 hours a day. During winter, some locks will be closed for maintenance and the status has to be checked with the Environment Agency.

The locks at the upper end of the river, from St John's Lock to King's Lock, are manually operated. All other locks on the Thames are hydraulically operated. All locks can be operated by boat crews outside manning hours, although many of the hydraulic locks must be operated manually in this mode. The Environment Agency has in recent years been modifying the hydraulic locks to allow boater operation of the power system when the lock keeper is not present

Locks are popular visitor attractions, and many serve refreshments. Locks were often built adjacent to islands and therefore many are situated in remote locations, hard to find and can only be reached on foot.


The Environment Agency has the responsibility of managing the flow of water along the length of the river to prevent flooding on particular reaches. The volume and speed of water down the river is managed by adjusting the gates at each weir. Occasionally this can result in a very fast stream rendering navigation more hazardous. These conditions are indicated by yellow or red warning boards on the lock gates. The Agency cannot legally stop navigation when the red boards are out, but continuing to travel is inadvisable and may invalidate a boater's insurance.

Occasionally flooding is unavoidable, and the Agency issues Flood Warnings with four levels of severity - Flood Watch, Flood Warning, Severe Flood Warning and All Clear. In recent years the Salmon Conservancy has been installing fish ladders at weirs to allow salmon to travel up river.

Today the weirs are often used recreationally by kayakers and canoeists for activities such as whitewater slalom and playboating. Specifically, Hambledon Weir and Boutler's Weir have EA sanctioned modifications made to them for such use.


The locks and weirs, in effect, break the river up into 45 lakes or lock reaches. Each lock controls the reach above it and thus identifies it. Each reach has its own character and points of interest.

Many reaches host regattas and other events and these are coordinated through a River User’s Group for the reach. The Environment Agency may close all or part of a reach for an event, but most regattas only require one side of the river which may then be closed off.

When the motive power for boats was provided by horses, a towpath was needed on the bank side. This towpath has formed the basis for the Thames Path which runs between the source and mouth of the river. The path runs between locks and is therefore often the main means of access on land. Where the towpath changes from one side of the river to the other ferries were once provided. These have now almost all disappeared and the Thames Path has to be diverted to the nearest bridge, often a considerable distance, to cope with this.

List of locks and weirs

There follows a list of locks and weirs in upstream to downstream order, from source to sea.
*St John's Lock (1790)
*Buscot Lock (1790)
*Grafton Lock (1896)
*Radcot Lock (1892)
*Rushey Lock (1790)
*Shifford Lock (1898)
*Northmoor Lock (1896)
*Pinkhill Lock (1791)
*Eynsham Lock (1928)
*King's Lock (1928)
*Godstow Lock (1790)
*Osney Lock (1790)
*Iffley Lock (1631)
*Sandford Lock (1631)
*Abingdon Lock (1790)
*Culham Lock (1809)
*Clifton Lock (1822)
*Day's Lock (1789)
*Benson Lock (1788)
*Cleeve Lock (1787)
*Goring Lock (1787)
*Whitchurch Lock (1787)
*Mapledurham Lock (1778)
*Caversham Lock (1778)
*Sonning Lock (1773)
*Shiplake Lock (1773)
*Marsh Lock (1773)
*Hambleden Lock (1773)
*Hurley Lock (1773)
*Temple Lock (1773)
*Marlow Lock (1773)
*Cookham Lock (1830)
*Boulter's Lock (1772)
*Bray Lock (1845)
*Boveney Lock (1838)
*Romney Lock (1798)
*Old Windsor Lock (1822)
*Bell Weir Lock (1817)
*Penton Hook Lock (1815)
*Chertsey Lock (1813)
*Shepperton Lock (1813)
*Sunbury Lock (1812)
*Molesey Lock (1815)
*Teddington Lock (1811)
*Richmond Lock (1894)

Additionally, Blake's Lock is located on a reach of the River Kennet that is administered by the Environment Agency as part of the River Thames, and is often counted as a Thames Lock. It is the only manual Thames lock below Oxford.

ee also

* Thames Barrier
* Crossings of the River Thames
* Islands in the River Thames

External links

* [http://www.visitthames.co.uk/uploads/a_users_guide_to_the_River_thames.pdf The must have guide for all Thames users] (published by the Environment Agency)
* [http://www.environment-agency.gov.uk/ Environment Agency]
* [http://www.the-river-thames.co.uk/locks.htm Floating down the river]

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