Horizontal water movement in a wave is usually less than the wavelength (tides, which are waves, only move water inland because their wavelengths are very long). At the place bores form however, the horizontal water movement in waves gets further and further, as the crests get higher and faster relative to the bed. Eventually the water starts to move horizontally and a bore forms in which the water movement is horizontal at the speed of the bore* (that is, supercritical: moving at the speed of local waves, carrying them along, rather than subcritical where waves move across the water). This is a much more efficient and speedy way of distributing the tidewater than the standard tide wave, which is butressed by the water in the river. However, the bore can look wave-like. This is partly a surface expression of regular structures within the bore caused by the river water trying to escape through it* (see Bore Structure), but the fact that the bore rises when the river depth drops* suggests a more traditional wave-nature. Because of this, the bore can have a complex relationship with the tidal waters (see evidence quoted in Chanson*).