Most waves in the ocean are caused by wind. An ocean wave is an irregularity on the surface of a body of water usually generated by wind. Wind is moving air and as this moves over the ocean it can cause water to pile up. The size of waves is not determined by just one factor. The wind speed as it blows over the water can produce high energy waves. The energy is also determined by the fetch. This is the distance in open water which the wind is able to blow over the water.