Canalization involves straightening a natural watercourse, giving it a standardized cross-section, and also constructing weirs in this river. As a result, the watercourse takes on the character of a canal with a regulated water level. When only the cross-section is adapted and the river is straightened, it is referred to as "normalization". In this case, the course of the river's summer bed is often determined with groynes. The Dutch Waal is a normalized river, whereas the Maas is a canalized river.

The purpose of canalization is twofold: on the one hand, to rapidly drain water to reduce waterlogging in the agricultural areas upstream, and on the other hand, to retain water at a desired level with the help of weirs. Rivers have been partially canalized to facilitate navigation, and some have been shortened by many dozens of kilometers as a result.