A flood plain is the flat land adjacent to rivers, lakes, or streams that is naturally subject to periodic flooding. Flood plains serve important environmental functions: absorbing floodwaters, reducing downstream flood peaks, filtering sediments and pollutants, and providing habitat. However, their flat terrain and fertile soil make them attractive for development, creating significant flood risk when buildings occupy flood-prone land. Land use planning typically restricts development in flood plains—official plans may prohibit new construction or require flood-proofing measures. Flood plain mapping identifies these areas, though many Canadian communities lack current maps. Development in flood plains not only puts occupants at risk but can worsen flooding for others by displacing water that would otherwise spread across the plain. Flood plain policies balance property rights against public safety and the costs of disaster recovery.