Many of the dams in the Mississippi headwater area were built for logging. Logging companies would save up the spring runoff water, then use it throughout the year to power saws and to float logs down stream. After the logging was over, the dams were used to augment the shipping season by releasing water during the months when the river was normally low. This resulted in lake levels that would vary widely. That wasn't a problem until people started to move in along the lake shore. In the dust bowl years, the lakes were nearly empty in fall, and there was little spring runoff water to fill the lakes. After that experience, the dam operations were changed to more closely regulate lake level and provide recreational opportunities.
