Small waves at the surface plays a role.
Surface Waves at sea are mainly caused by the wind, but also earthquakes, volcanic eruptions and tidal waves cause. At wind speeds below 2 knots on flat water forms almost immediately by the surface waves just as quickly disappear if the wind dies down. Above the two nodes are formed stable gravitational waves. This swell grows as the wind increases. The period of this lies in an area of approximately 10 seconds. Once the wind drops or when the waves come out of the wind field, refers to swell. Since longer waves are faster than shorter plants (frequentiedispersie), will be a point outside the wind field first a long period swell arriving which can rise to about 30 seconds, followed by a shorter wave. By friction and the fan (richtingdispersie) loses the swell of energy and height. Because shorter waves are longer to reach a certain point, the energy loss is relatively larger, so only the long swell remains. The extinction of this is so slow that it continues to swell a coastal reached.
Waves are unlike wind and currents are not influenced by the Earth's rotation.
Source : http://nl.wikipedia.org/wiki/Oppervlaktegolf_%28vloeistofdynamica%29