Changes in the shape of the bottom of lakes, rivers, or impoundments, especially those that influence fish behavior. This is probably the most misunderstood word in bass fishing. Structure is a feature on the bottom of the lake. Some examples of structure are creeks, humps, depressions, sandbars, roadbeds, ledges, and drop offs. Some examples that are not structure: a stump, tree, or brush pile (these are cover).