A flood warning system has a gauge unit adapted to be positioned adjacent to a waterway and a display adapted to be positioned away from the waterway and adjacent to a roadway. The gauge unit has a plurality of sensors arranged in vertically-spaced relation within a housing of the gauge unit. The housing has a fluid inlet adapted to allow water to enter the housing when a level of water in the waterway raises above a low position. The plurality of sensors are adapted to detect a level of water within the housing of the gauge unit. The display has a warning indicator thereon. The display is cooperative with the gauge unit such that the warning indicator is actuated when the level of water in the housing of the gauge unit is above one of the plurality of sensors.