A levee is a man-made structure, usually an earthen embankment, designed and constructed in accordance with sound engineering practices to contain, control, or divert the flow of water so as to reduce the risk from temporary flooding. Levees can be naturally occurring ridge structures that form next to the bank of a river or be an artificially constructed fill or wall that regulates water levels. The purpose of a levee is to keep the course of rivers from changing and to protect against flooding of the area adjoining the river or coast. Levees are typically little more than a mound of less permeable soil, like clay, wider at the base and narrower at the top, and they run in a long strip, sometimes for many miles, along a river, lake, or ocean. Levees can be covered with vegetation such as Bermuda grass to protect their surface from erosion, and on the river side, erosion from strong waves or currents presents an even greater threat to the integrity of the levee.