Cromwell Lock is a large navigation lock on the River Trent in Nottinghamshire, UK. The first lock to be built on the site was constructed by the Trent Navigation Company, having been authorised by an Act of Parliament obtained in 1906. Construction began in late 1908, as soon as the Company had raised sufficient capital. The lock was extended in 1935, when an extra pair of gates were added downstream of the main lock, effectively forming a second lock.