The underwater cross-section of a ship in the channel is limited by the fairway depth and width (bridges may create restrictions for the height above the waterline).
The fairway depth of a river varies with the season, so some standardized depth value is used, usually the one corresponding to the low navigable water level (LNWL) defined as the water level that the river stays above during almost the entire navigation season: statistically, the level shall stay below the LNWL for 20 ice-free days per year, corresponding to 5-6% of the ice-free period on European rivers.
[7] The courts, however, use an expanded definition and include into the scope of Title 33, for example, waters "frequented by small, pleasure-fishing crafts".
[9] Many major European rivers (e.g., Rhine, Danube, Moselle, Meuse, and Sava) have long-established systems for waterway management.
[12] Inland waterways in the United states are managed by the US Army Corps of Engineers (USACE).