Lock (water navigation)

Not to be confused with Loch. "Gate (water transport)" redirects here; not to be confused with Water gate.

Canal lock and lock-keeper's cottage on the Aylesbury Arm of the Grand Union Canal at Marsworth in Buckinghamshire, England

Lock on the River Neckar at Heidelberg in Germany

Three Gorges Dam lock near Yichang on the Yangtze river, China

A lock is a device used for raising and lowering boats, ships and other watercraft between stretches of water of different levels on river and canal waterways. The distinguishing feature of a lock is a chamber in a permanently fixed position in which the water level can be varied. In a caisson lock, a boat lift, or on a canal inclined plane, it is the chamber itself (usually then called a caisson) that rises and falls.

Locks are used to make a river more easily navigable, or to allow a canal to cross land that is not level. Over time, more and larger locks have been used in canals to allow a more direct route to be taken.