definition
strict definition
canal
A stable artificial channel of navigable water made by excavation with retained land on both sides.
A canal is a stable and navigable linear channel of water constructed by excavating its path and ensuring retention of the land on both sides.
Excavation creates the route and the retained sides define its linear channel. Navigability is part of the stated form rather than merely the presence of water.
A trench has a waterless excavated form. An artificial pond is a confined body rather than a linear navigable route.