What does “full-fetch” winds mean?

Dear Tom,

I often hear you use the term “full-fetch” winds. Could you tell me what that means?

Thanks,
Aaron Duncan

Dear Aaron,
Wave heights are limited by fetch, the distance the wind can blow across the water. Lake Michigan’s largest waves have been measured at just over 20 feet at the south end of the lake, generated by long-duration full-fetch north winds blowing down the entire 300-mile length of the lake with speeds in excess of 55 mph. Lake Superior, boasts the highest waves on the Great Lakes with heights approaching 30 feet in violent fall storms like the one that sank the Edmund Fitzgerald in 1975. On the virtually unlimited fetch and expanse of this planet’s oceans, waves can tower to more than 50 feet, and in extreme conditions approach 100 feet.