Fetch, and why some lakes get rough so fast

Fetch is the distance wind travels across open water without hitting land. Waves grow with three things: how strong the wind is, how long it has been blowing, and how much fetch it has.

Why it matters on lakes

On a small pond the fetch is a few hundred yards, so even a 20 kt wind only makes a short, choppy ripple. On a large reservoir the same wind blowing down a 10-mile reach can build steep waves of 3 ft or more. Because lake waves are short and close together, they feel rougher than ocean swell of the same height.

The Great Lakes have fetch measured in hundreds of miles. Waves there behave like the sea, which is why the National Weather Service issues marine forecasts for them.

Using it to pick your spot

1. Look at the forecast wind direction. Wind is named for where it comes from, so a north wind blows toward the south.
2. Find the shore the wind is blowing from. Water there is sheltered, with little fetch.
3. The opposite, downwind shore takes the full build of waves.

On a windy day, launching from the upwind shore and staying in its lee keeps paddlers and small boats in flatter water. On a long, narrow lake, a wind aligned with its length is much worse than a wind blowing across it.

Each Lakeglance forecast shows wind direction hour by hour, with an arrow pointing the way the wind is blowing.