Flooding associated with recent extreme weather events has caused levee failures in Japan, which has many steep rivers, resulting in extensive damage, such as inundation of residential and agricultural lands. Many levees have been built by adding fill to older ones, and the soil structure inside the levees is complex. The interior of the levees cannot be determined without modification to the ground surface. Conventional inspection methods (ex. GPR) can only inspect to a maximum depth of several meters and not reveal any hidden hazards, so reinforcement and other safety measures are usually taken only after an accident has occurred. Therefore, we wondered if it would be possible to detect the location of deformation inside the levee and evaluate the safety of the levee in order to prevent flood disasters, using the technology of cosmic-ray imaging with nuclear emulsion films that has been used to image the inner structure of nuclear reactors and pyramids. In this presentation, we report on the observation of the density distribution inside the levee by installing nuclear emulsion films in the culvert, which was started in the fall of 2021. Seven detectors were installed in a flume pipe approximately 70 m long, and this observation was throughout the year. Muon flux of all detectors reflects the overburn thickness, and penetration rate also clearly indicates the amount of accumulated material including peripheral equipments. In addition, we found that three spots of low density were consistent with the location and size of handholes buried in the levee from the data of six months.