Chertsey Lock is a lock on the River Thames in England, on the northern Middlesex bank near Chertsey (which is on the opposite side of the river) in north-west Surrey. The lock is about 200 yards upstream of the picturesque Chertsey Bridge. It was first built by the City of London Corporation in 1813.
The lock adjoins a small thin island connecting to Chertsey Weir, which is not pedestrianised.
There used to be problems upstream of the lock's position because of the shallows known as Laleham Gulls, and various proposals were put forward to resolve them. There was a survey for a lock in 1793, but it was disallowed by parliament. In 1805 there was another proposal for a cut along the length of the current reach, with a pound lock at the lower end, but this was resisted by local landowners. A lock was authorised by parliament in 1810 a short way upstream, but when Lord Lucan asked to have the lock out of his view, a new Act in 1812 authorised it at the present lower site. The lock was opened in 1813 with the lock-house effectively on the Middlesex bank (although technically in Surrey because the course of the stream had been altered. The lock was lengthened in 1893 and again in 1913. It was then built with two compartments, but the centre gates have since been removed.
Access to the lock
The lock is easily accessible, being on the Middlesex bank, immediately adjacent to Thames Side road and a short distance from Chertsey Bridge and the Kingfisher pub.
Reach above the lock
Shortly upstream of the lock, the river is crossed by the M3 Chertsey Bridge carrying the M3 motorway high overhead. The Middlesex bank has gravel pits out of sight and then park land until it reaches Laleham, where there are riverside houses. From an inlet at Laleham, 200 million imperial gallons (910,000 m3) of water are pumped into the Queen Mary Reservoir each day.
The Surrey bank is wild and open with a very small reservoir and pumping station beyond it. There is then a stretch of housing interspersed with boatyards, until short of Penton Hook. Before Penton Hook Lock, the backwater curves round Penton Hook Island to some marinas. This is the start point of the Abbey River backwater which rejoins the Thames below Chertsey Lock. Burway Rowing Club is based at Thameside at Laleham on the reach and Burway Junior Regatta and Burway Head races take place from the area beneath the M3 Motorway Bridge.
The Thames Path follows the Middlesex bank all the way to Penton Hook lock.
|Next lock upstream||River Thames||Next lock downstream|
|Penton Hook Lock
3.13 km (1.94 mi) 
3.32 km (2.06 mi)
- "Environment Agency Dimensions of locks on the River Thames". web page. Environmental Agency. 8 November 2012. Retrieved 18 November 2012. Dimensions given in metres
- Fred. S. Thacker The Thames Highway: Volume II Locks and Weirs 1920 - republished 1968 David & Charles
- Spelthorne Borough Council A Walk round Laleham village Archived November 3, 2007, at the Wayback Machine.
- "Environment Agency Distances between locks on the River Thames". web page. Environmental Agency. 19 November 2012. Retrieved 22 November 2012. Distances given in km.