A flood prevention barrier is an object designed to keep the flow or intrusion of water from a river or any standing or flowing body of water from getting some place or area wet. The same barrier may serve the dual purpose of flood prevention and reservoir formation.

The protected area is kept from being wetted by water arriving from a standing or flowing body. The barrier can address flow or intrusion.

The same object can retain a usable water supply. Flood prevention and reservoir formation are therefore compatible purposes.