Levees are wide walls formed along river banks to help keep the water in the river bed and prevent flooding. In the spring time or after heavy rains, many rivers overflow into the low lying lands around them. When they overflow they still carry dirt and sediment with them. The flooded water cannot move as fast as it did in the river; therefore, it begins to drop the dirt along the river bank. Eventually the dirt and debris accumulate and form natural levees.
   These natural levees help to protect the people who live along the river from floods, as the water must reach a higher level to go over the levee. In many places, especially along the Mississippi River, these natural levees are not enough to protect the people, and wide walls or man-made levees are built along the river to keep it from flooding. They are made of sandbags and banked earth.