A levee is a natural or artificial flood bank that follows along a river or canal path. In the case of a natural levee, such an occurrence is created when a river floods over the bank and deposits sediment and causes the banks to be higher than the floodplain. In the case of a man-made levee, its purpose is to prevent flooding, contain the water flow and/or increase the water speed.

Also known as a stop wall, dike, dam or storm barrier, a levee can be found along lakes, rivers or the sea. Generally made of soil, some man made levees are reinforced by rocks or concrete to prevent erosion. A levee is occasionally used as a military defense, as well. There is no set height for a levee; the height usually varies between 10-30 feet (3-10 m). An emergency levee, such as that to be used in the event of flood, can be created by sandbags.

In the Southern and Midwestern areas of the U.S., levee is the commonly used term. In Europe and Canada, a levee is most likely to be known as a dike. Although the terms are often used interchangeably, the definition is slightly different. In the Netherlands, a system of dikes divert flooding waters from large bodies of water. However, along the Mississippi River, a system of levees restrains flooding waters from lakes and stream. A levee might also be referred to as an embankment.

A levee failure occurs when a break, also known as a breach, occurs. As part of the levee breaks away, it allows water to flow through the opening. Another type of failure occurs when water flows over the top of the levee. Sand boils can also occur during a breach. A sand boil results when the rising pressure of the water flowing through the pores in the soil is stronger than the downward pressure of the soil.