Leonardo da Vinci helped develop the miter lock, a canal device whose angled gates seal against water pressure.
A miter lock has two gates that meet in a point facing the higher water level. Water pressure pushes the gates together, helping them form a watertight barrier. Boats can then pass between water levels as the chamber is filled or emptied.
Leonardo worked on canal engineering in Milan and is associated with improvements to canal locks, including practical gate and chamber arrangements. The basic idea was part of a broader history of canal technology rather than a wholly isolated invention created by one person.
A lock is not the same as a dam or aqueduct. A lock raises or lowers boats through a controlled chamber, while an aqueduct carries water and a dam stores or regulates it.