The length of stretches of water, not part of the sea, which by natural or man-made features are suitable for navigation, primarily by inland waterway vessels. This term covers navigable rivers, lakes, canals and estuaries.
The length of rivers and canals is measured in mid-channel. The length of lakes and lagoons is measured along the shortest navigable route between the most distant points to and from which transport operations are performed. A waterway forming a common frontier between two countries is reported by both.