While sea walls prevent erosion as the base of the bluff, and also stabilize the upper part of the bluff, they do have drawbacks. In addition to the cost, they reflect the energy of incoming waves, which then remove sand from the beach. Also, they reflect wave energy onto the surrounded bluffs, causing increased erosion where the sea wall ends. (This is particularly obvious when one visits the site in person, and can examine the sea walls closely.) Finally, by preventing erosion, the sea walls deprive the beach of an important source of sand. This sand is not only important for its recreational uses and aesthetic appeal, but also acts as a buffer to incoming waves. For all these reasons many scientists have distinctly mixed opinions concerning the use of sea walls to prevent coastal erosion.