This is the length of the exterior shoreline around a lake - measured at the lake's normal elevation. The shoreline length can be considerably shorter or longer when lake water levels are lower or higher than normal.
A lake with many coves has a much longer shoreline than a lake of similar surface area that is nearly circular in shape.
When known, the shoreline miles that we report in our statistics include only the lake's exterior shoreline, and exclude the shorelines of islands located within a lake's boundaries. In lakes with many islands, those islands' combined shorelines may exceed a lake's exterior shoreline.
You can find many of the world's longest-shoreline lakes on Lakelubbers.