Great Lakes shorelines continue to evolve, and many of them have been retreating for thousands of years. As the shoreline has retreated, there has been a corresponding erosion (or down-cutting) of the lake bed in many places. Stopping these natural processes is complex because of the consequences to other sections of the shoreline, the variability in shoreline soils and geometry, and the complexity of the processes that erode the shoreline. Natural processes (including the freezing and thawing of water) impact the function of shore protection structures.