Locks and weirs on the River Thames

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The English River Thames is navigable from Cricklade (for very small, shallow boats) or Lechlade (for larger boats) to the sea, and this part of the river falls 71 meters (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.

Mapledurham Lock


The weir at Mapledurham Lock
Mapledurham Watermill

From ancient times there were many obstructions across the Thames, for fish-pounds and millers' weirs. They are referred to by Asserius Menevensis in the ninth century and Magna Carta (1215) states that "weirs, for the time to come, shall be demolished in the Thames and Medway, except on the sea coast." It appears this never happened.[1] In 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 led 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.[2]

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 and at Swift Ditch near Abingdon. In 1751, the Thames Navigation Commissioners were established and built eight locks between Shiplake Lock and Boulters lock between 1770 and 1773. The opening of the Thames and Severn Canal from Lechlade in 1789 led to the building of many of the locks upstream of Shiplake. The six locks built by the City of London Corporation on the tidal section below Staines between 1811 and 1815 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. In 1908 an Act transferred responsibility for the Thames from a point 350 yards (320 m) below Teddington Lock to the Port of London Authority, and this included Richmond Lock.[2] 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.


Penton Hook Lock with City of London arms on the House. The green box is the hydraulic control system
Goring Lock demonstrates the common juxtaposition of weir, lock island, lock keeper's house and lock
Choice of Yellow and Red warning boards which are placed on lock gates when navigation is hazardous
Kayaker at Boulter's Weir


From the head of navigation at Cricklade 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 provide navigable water depths and also regulating and promoting navigation on the river. 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.

Most of the Environment Agency's locks and weirs are staffed by a lock keeper, who often 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 and volunteers 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 long Kingston reach of the non-tidal river from Hampton Court to the tideway, is staffed 24 hours a day. During winter, some locks will be closed for maintenance and the status has to be checked with the Environment Agency.[3]

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, except Teddington, can be operated by boat crews outside manning hours, using the adapted system of "public power", which allows boaters to use the hydraulic machinery at reduced power, except during the hours of darkness.

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. Many locks also have moorings that can be used overnight, and some include electric charging points for electric powered boats.

All the locks have obvious access from the Thames Path, except for Whitchurch Lock which is within an island and only accessible by boat; Cookham Lock requires a 1km diversion from the Thames Path; and Marlow Lock requires a short diversion.


The Environment Agency has the responsibility of managing the flow of water along the length of the river to prevent flooding on particular reaches and to maintain navigation depths. The volume and speed of water down the river is managed by adjusting the gates at each weir. Occasionally this can result in a fast stream rendering navigation more hazardous. These conditions are indicated by yellow or red warning boards on the lock gates and the status of all locks is published by the Agency.[4] 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 three levels of severity - Flood Alert, Flood Warning, and Severe Flood Warning.[5]

In recent years the Salmon Conservancy has been installing fish ladders at weirs to allow salmon to travel up river.

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


The locks and weirs, in effect, break the river up into 44 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.[6] 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 boats were horse drawn, 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.

Foot crossingsEdit

All of the Thames locks have walkways on top of the lock gates, so except at Whitchurch Lock one can cross to the lock island from the adjacent bank. Upstream of Wallingford, many locks also have walkways on top of the weir to cross the whole river. Downstream of Wallingford, Caversham Lock and Boulters Lock have footbridges nearby, and Hambleden Lock has a walkway on top of the weir, but the other locks below Wallingford do not allow river crossing on foot.

List of locks and weirsEdit

St John's lock - the beams indicate manual operation
The footbridge at Marsh Lock
Paired locks at Sunbury
Richmond half tide barrage, Lock by far bank

The list of locks, weirs and ferries is given in upstream to downstream order, from source to sea.[7][8] Most of the older flash locks have disappeared and there are only three ferries still operating (Weybridge, Hampton and Hammerton's). Nearly all of the older weirs and most of the current ones once had associated mills, fifteen of which are mentioned in the Domesday book, but very few of these survive.[9] A few weirs had bucks for catching eels.

Lock Date Recorded date of flash lock Fall Distance from next lock up Earlier weirs in this reach Ferries
St John's Lock 1790 1775 0.85 m (2.8 ft)
Buscot Lock 1790 1.69 m (5.5 ft) 1.85 km (1.15 mi)
Grafton Lock 1896 1762 (Day's/Lower Hart) 1.11 m (3.6 ft) 5.37 km (3.34 mi) Farmer's, Harts
Radcot Lock 1892 1746 (Beck's, Clare's or Buck's) 1.48 m (4.9 ft) 2.98 km (1.85 mi) Old Eye
Rushey Lock 1790 1.82 m (6.0 ft) 4.23 km (2.63 mi) Old Nan's Rushey
Shifford Lock 1898 1762 2.23 m (7.3 ft) 6.92 km (4.30 mi) Tadpole (Kent), Thames, Ten foot, Shifford Upper, Duxford Duxford
Northmoor Lock 1896 (Hart's Weir) 1.24 m (4.1 ft) 7.63 km (4.74 mi) Limbre's Ridge's (Hart's)
Pinkhill Lock 1791 Pre-1791 1.05 m (3.4 ft) 6.21 km (3.86 mi) Ridge's (Langley), Ark, Skinner's Bablock Hythe
Eynsham Lock 1791 0.84 m (2.8 ft) 2.38 km (1.48 mi)
King's Lock 1890? 1541 0.77 m (2.5 ft) 4.37 km (2.72 mi) Clay
Godstow Lock 1790 1.57 m (5.2 ft) 1.81 km (1.12 mi)
Osney Lock 1790 1227 1.89 m (6.2 ft) 3.87 km (2.40 mi) Medley (Binsey)
Iffley Lock by 1632 1585 0.81 m (2.7 ft) 3.73 km (2.32 mi) Folly Iffley
Sandford Lock 1632 (enlarged 1793) 2.69 m (8.8 ft) 2.7 km (1.7 mi)
Abingdon Lock 1790 1316 1.89 m (6.2 ft) 7.38 km (4.59 mi) Nuneham Thrupp
Culham Lock 1638 (moved 1809) 1580 2.41 m (7.9 ft) 4.15 km (2.58 mi) Culham old (1638 on Swift ditch), Swift
Clifton Lock 1812 1.03 m (3.4 ft) 4.52 km (2.81 mi) Culham
Day's Lock 1789 1580 1.58 m (5.2 ft) 4.8 km (3.0 mi) Dorchester, Clifton
Benson Lock 1788 1746 1.87 m (6.1 ft) 6.37 km (3.96 mi) Shillingford, Keen Edge
Cleeve Lock 1787 1580 0.89 m (2.9 ft) 10.46 km (6.50 mi) Pollington's, Chalmore Lock, Moulsford (lock) Leather Bottle, South Stoke, Littlestoke, Chalmore, Benson
Goring Lock 1787 1538 1.77 m (5.8 ft) 1 km (0.62 mi) Streatley
Whitchurch Lock 1787 1580 1.01 m (3.3 ft) 6.55 km (4.07 mi) Hart's lock Gatehampton
Mapledurham Lock 1777 1300 2.05 m (6.7 ft) 3.67 km (2.28 mi)
Caversham Lock 1778 1493 1.44 m (4.7 ft) 7.08 km (4.40 mi) Chawsey Purley (2)
Sonning Lock 1773 1580 1.63 m (5.3 ft) 4.23 km (2.63 mi) Breach's
Shiplake Lock 1773 1746 1.55 m (5.1 ft) 4.68 km (2.91 mi) Wargrave, Bolney
Marsh Lock 1773 1580 1.33 m (4.4 ft) 4.8 km (3.0 mi) Beggar's Hole (Bolney), Lashbrook, Wargrave
Hambleden Lock 1773 1338 1.44 m (4.7 ft) 4.59 km (2.85 mi) Aston
Hurley Lock 1773 1580 1.05 m (3.4 ft) 5.89 km (3.66 mi) Mednam Medmenham
Temple Lock 1773 1580 1.23 m (4.0 ft) 1.03 km (0.64 mi) Temple
Marlow Lock 1773 1585 2.16 m (7.1 ft) 3.13 km (1.94 mi)
Cookham Lock 1830 1.3 m (4.3 ft) 6.44 km (4.00 mi) Cookham Upper, Spade Oak
Boulter's Lock 1772 (moved 1828) 1580 2.39 m (7.8 ft) 3.35 km (2.08 mi) My Lady, Hedsor
Bray Lock 1845 1328 1.46 m (4.8 ft) 3.43 km (2.13 mi)
Boveney Lock 1838 1375 1.47 m (4.8 ft) 5.1 km (3.2 mi) Boveney
Romney Lock 1797 2.01 m (6.6 ft) 3.75 km (2.33 mi) Gill's bucks Windsor
Old Windsor Lock 1822 1300 1.74 m (5.7 ft) 4.83 km (3.00 mi) Datchet
Bell Weir Lock 1817 1300 1.82 m (6.0 ft) 4.94 km (3.07 mi) Magna Carta Island
Penton Hook Lock 1815 1.22 m (4.0 ft) 4.33 km (2.69 mi) Savory's Tims', Egham
Chertsey Lock 1813 1.22 m (4.0 ft) 3.13 km (1.94 mi) Laleham
Shepperton Lock 1813 2.03 m (6.7 ft) 3.32 km (2.06 mi)
Sunbury Lock 1812 1623 1.87 m (6.1 ft) 4.75 km (2.95 mi) Ballinger's Shepperton Church, Weybridge
Molesey Lock 1815 1.87 m (6.1 ft) 4.79 km (2.98 mi) Hampton
Teddington Lock 1811 2.68 m (8.8 ft) 7.74 km (4.81 mi) Kingston Surbiton, Ravens Ait, Thames Ditton
Richmond Lock 1894 2 m (6.6 ft) 4.9 km (3.0 mi) Hammerton's, Twickenham

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.

The tide flows as far as Teddington Lock: the weir at Richmond Lock is only used at low tide, to maintain the water level above it.

Chalmore Lock (1838) was removed in 1883.

See alsoEdit


  1. ^ Dix, Frank L. (1985), Royal River Highway, David & Charles, Newton Abbott, p. 12
  2. ^ a b Fred S. Thacker The Thames Highway: Volume 1 General History David & Charles 1968
  3. ^ Environment Agency, EA Winter Lock Closures and Repairs
  4. ^ Environment Agency River Thames River Conditions Archived 16 January 2009 at the Wayback Machine
  5. ^ "Check for flooding in England - GOV.UK".
  6. ^ See River User Groups Archived 4 August 2009 at the Wayback Machine
  7. ^ Thacker, Frederick S. (1968) [1920], The Thames Highway, vol. II: Locks and Weirs, David & Charles, Newton Abbott
  8. ^ 2012-13 Cruising Guide to the River Thames and Connecting Waterways, British Marine Federation
  9. ^ Thacker 1915, p. 156

External linksEdit