A river blocker is an artificial structure built to prevent the flow of a river. The most common types of river blockers are levees, dams, and dikes. A LEVEE is an embankment built along the banks of a river to prevent flooding. A DAM is a barrier constructed across a river to control the flow of water. A DIKE is a wall or embankment built to prevent flooding or hold back water. All three of these structures are used to block the flow of a river and can be used to protect areas from flooding.