A floodplain is a land area that will flood in a storm event that has a 1% chance of occurring in any given year. Floodplains are designated by the Federal Emergency Management Agency (FEMA) and cover parts of Cary, particularly along the Fox River, Cary Creek, and behind Lions Park.

The floodplain is composed of a floodway and a flood fringe. The floodway is typically determined to be the channel of a river or stream and the overbank areas adjacent to the channel. The flood fringe is the area to either side of the floodway that is subject to flooding, but conveys little or no flow. Most often, this community experiences flash flooding, which is less predictable than river flooding. There is little time to prepare for a flash flood, so pre-planning is essential for safety and home protection. In support of the National Flood Insurance Program (NFIP), the Federal Emergency Management Agency (FEMA) has undertaken an effort of flood hazard identification and mapping to produce Flood Hazard Boundary Maps, Flood Insurance Rate Maps, and Flood Boundary and Floodway Maps.