A waterway is any navigable body of water. These include rivers, lakes, seas, oceans, and canals. In order for a waterway to be navigable, it must meet several criteria:
- The waterway must be deep enough to allow the draft depth of the vessels using it;
- The waterway must be wide enough to allow passage for the beam width of the vessels using it;
- The waterway must be free of barriers to navigation such as waterfalls and rapids, or have a way around them (such as canal locks);
- The current of the waterway must be mild enough to allow vessels to make headway.
Vessels using waterways vary from small animal-drawn barges to immense ocean tankers and ocean liners, such as cruise ships.
Canals are waterways that are constructed to provide a new path of travel for vessels (as opposed to improving a natural waterway along its current course). At one time, canals were built mostly for small wooden barges drawn by horses
or other draft animals
. Today, major canals are built to allow passage of large ocean-going vessels (see Ship canal
A tidal waterway is one open to the sea and far enough downstream (close enough to the sea) to be subject to twice-daily (or daily, depending on the local tides) reversals of flow and variation in depth. Non-tidal waterways are either far enough upstream to be beyond tidal effects, or are separated from the sea or the tidal stretch of the same waterway by a barrier (usually a navigation lock).
In actuality, every body of any liquid on the face of the Earth is subject to tides—even a bird bath. However, only bodies of water susceptible to tidal changes noticeable to humans are included in the customary definition.