A flood stopper is a device or structure used to prevent flooding. Sandbags, dikes, and levees are all common flood stoppers. Sandbags are sacks filled with sand or soil that are used to block water from entering an area. Dikes are walls built along the banks of rivers or other bodies of water to prevent flooding. Levees are embankments built along rivers or coasts to protect against flooding. All three of these methods can be used to help stop floods.