Surf

Source: Port Covo pano | WikiMedia

As the swell approaches the coastline, the energy of the wave comes in contact with the ocean floor. The friction from this contact slows down the forward motion of the bottom of the wave.

The shallow water and the slower forward motion at the bottom of the wave cause the wavelength to shorten and the amplitude to increase. This process is called shoaling. The steeper the change in the ocean floor, the more pronounced wave height becomes. The surf zone is the area near the shoreline of lakes and oceans where the waves break.