Wind sea or simply sea is the wave disturbance raised by the wind blowing at the time of observation. Sea waves propagate in a direction within 10 degrees or so of the prevailing wind blowing and are still growing or sustained by the wind, in contrast to swell. The height of the sea waves is determined by the distance over which the wind has acted on the water in the same direction (called fetch), the average wind speed over the fetch, and the length of time the wind has been blowing. The height of sea waves varies from 1/13 to about 1/35 of their length.