St John's Lock, below the town of Lechlade, Gloucestershire, is the furthest upstream lock on the River Thames in England. The name of the lock derives from a priory that was established nearby in 1250, but which no longer exists. The lock was built of stone in 1790 by the Thames Navigation Commission.

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St John's Lock
St John's Lock, with Lechlade in the background
Waterway	River Thames
County	Gloucestershire
Maintained by	Environment Agency
Operation	Manual
First built	1790
Latest built	1905
Length	33.60 m (110 ft 3 in) [1]
Width	4.52 m (14 ft 10 in)[1]
Fall	0.85 m (2 ft 9 in)[1]
Above sea level	233 ft (71 m)
Distance to Teddington Lock	123 miles

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Legend
River Thames to Cricklade Thames and Severn Canal River Coln Usual limit of navigation Lechlade A361 Halfpenny Bridge St John's Lock weir A417 St John's Bridge weir River Leach River Cole River Thames

The main weir is downstream, just below St John's Bridge, where the River Cole and the River Leach join the Thames on opposite banks.

A statue of Old Father Thames by Raffaelle Monti is outside the lock house. The statue was commissioned in 1854 for The Crystal Palace's grounds, was later moved to the traditional source of the Thames at Thames Head, and then in 1974 relocated to St John's Lock.^[2] The statue is Grade II listed.^[3]

The need for a pound lock here arose from the opening of the Thames and Severn Canal upstream in November 1789. It was built by J. Nock in 1790, and in its early days complaints were made of tolls being evaded by bullying bargemen. The first lock house was built in 1830, the lock-keeper being required to give up residence at the Trout Inn in accordance with Commission's rule that lock-keepers should not be publicans. The lock was reported to be in a poor state by 1857 and in 1867 was repaired. In 1905 the lock was rebuilt and a new lock-keeper's bungalow built on the other side of the lock.^[4]

The lock can be reached easily from St John's Bridge which is about a mile out of Lechlade on the A417 road.

The river winds for three quarters of a mile to Lechlade, where it passes under Halfpenny Bridge (or Ha'penny Bridge), which is so named because it was once a toll bridge. Half a mile after Lechlade there is a connection to the former Thames and Severn Canal, which linked the Thames to the River Severn via the Stroudwater Navigation and the Gloucester and Sharpness Canal. The Thames and Severn Canal is the subject of a restoration plan, and so navigation beyond Lechlade may one day be possible again. The River Coln also joins the Thames at the canal junction, where there is sufficient room to wind a 70 ft narrowboat with care. There are no more locks upstream on the River Thames, with Lechlade normally considered to be the end of the navigable river, but there is a right of navigation as far as Cricklade, and small craft may be able to travel for a further three miles beyond Lechlade when there is plenty of water.^[5]

The Thames Path follows the remaining towpath along the southern bank past Lechlade to Inglesham, extending as far as the connection with the now disused Thames and Severn Canal, one and a half miles upstream.^[6]

• Locks on the River Thames