A huayco or huaico (from the Quechua wayqu, meaning "depth, valley") is a Peruvian term that refers to a flash flood caused by torrential rains occurring high in the mountains, especially during the weather known as El Niño.
National forests such as the San Matías–San Carlos Protection Forest were created in Peru to protect vegetation, which reduces runoff, and prevent huaycos.
The indigenous Mapuche residents of Lo Barnechea, in present-day Santiago Province, Chile, were called Huaicoches in their Mapudungun language: Huaico (flash flood) and che (people).