Fetch can be described as the length of the wind action. In a certain point, fetch can be seen as the direct distance, in the direction of the wind and on the surface of the water, between this point and the point where the wind effect started to take place. In areas where the fetch is not restricted (e.g. open sea), there is a dominant fetch and small changes in wind direction don’t significantly change fetch length or the direction of the generated wave. On the other hand, for wind directions parallel to the shore and mainly for lakes, lagoons or estuaries, a small variation in the wind direction can generate significant changes in the wind’s length of action. In these areas there is not a predominant direction for fetch. In order to calculate the effective fetch it is then necessary to take into account the local morphology of the study area considering several directions, each one with a different weight. Thus, for the same wind direction, a point with more obstacles in the near directions has assigned a smaller fetch than a point with more water length in the same directions.